Discontinuation of prophylaxis for Pneumocystis carinii pneumonia in HIV-1-infected patients treated with highly active antiretroviral therapy

BACKGROUND: Prophylactic drugs for Pneumocystis carinii pneumonia (PCP) are strongly recommended for HIV-1-infected patients with CD4 cell counts of less than 200 cells/microL. Because of the highly active antiretroviral therapy (HAART) currently available, we speculated that prophylaxis can be discontinued in patients with CD4 cell counts of more than 200 cells/microL. METHODS: In this prospective observational study, PCP prophylaxis (primary or secondary) was discontinued in HIV-1-infected patients whose CD4 cell count had increased above 200 cells/microL (documented twice with an interval of at least 1 month) as a result of HAART. Patients and their CD4 cell counts were monitored every 3 months. The primary endpoint of the study was the occurrence or reoccurrence of PCP. FINDINGS: 78 patients were enrolled: 62 patients were receiving prophylaxis for primary prevention of PCP and 16 patients for secondary prevention of PCP. At the time of discontinuation of prophylaxis, the mean CD4 cell count was 347 cells/microL, and HIV-1-RNA was not detectable in 61 patients. The lowest mean CD4 cell count during prophylaxis was 79 cells/microL. Patients stopped prophylaxis 9.8 (SD 6.4) months after they started HAART. The mean follow-up after discontinuation of prophylaxis was 12.7 (SD 7.6) months, and none of the patients developed PCP (97.5% one-sided CI 0-4.4%). INTERPRETATION: The preliminary results of this study indicate that PCP prophylaxis can be stopped safely in HIV-1-infected patients whose CD4 cell counts have increased above 200 cells/microL after treatment with HAART.     

Mifepristone. Auxiliary therapeutic use in cancer and related disorders

A pilot study was carried out to assess the safety and antigen-presenting properties of allogeneic or autologous dendritic cells (DCs) in six HLA-A2+, HIV-infected patients. Allogeneic DCs obtained from the peripheral blood of HLA-identical, HIV-seronegative siblings were pulsed with recombinant HIV-1 MN gp160 or synthetic peptides corresponding to HLA-A2-restricted cytotoxic epitopes of envelope, Gag, and Pol proteins. The antigen-pulsed cells were infused intravenously six to nine times at monthly intervals and HIV-specific immune responses were monitored. One allogeneic DC recipient with a CD4+ T cell count of 460/mm3 showed increases in envelope-specific CTL- and lymphocyte-proliferative responses, as well as in IFN-gamma and IL-2 production. Another allogeneic DC recipient with a CD4+ T cell count of 434/mm3 also showed an increase in HIV envelope-specific lymphocyte-proliferative responses. A recipient of autologous DCs with a CD4+ T cell count of 730/mm3 showed an increase in peptide-specific lymphocyte-proliferative responses after three infusions. Three other allogeneic DC recipients with CD4+ T cell counts <410/mm3 did not show increases in their HIV-specific immune responses. No clinically significant adverse effects were noted in this study and CD4+ T cell numbers and plasma HIV-1 RNA detected by RT-PCR of all six patients were stable during the study period. Thus, both allogeneic and autologous DC infusions were well tolerated and in patients with normal or near normal CD4+ T cell counts administration of these antigen-pulsed cells enhanced the immune response to HIV. However, since no effect on viral load was observed there was no evidence that this approach provided clinical benefit.     

2-chlorodeoxyadenosine induces durable remissions and prolonged suppression of CD4+ lymphocyte counts in patients with hairy cell leukemia

A number of effective treatments are available for patients with hairy cell leukemia (HCL). 2-Chlorodeoxyadenosine (2-CdA) induces more than 80% complete responses, but is associated with profound suppression of CD4+ lymphocyte counts. However, the duration of each is uncertain. We have analyzed a previously reported cohort of 40 patients who had responded to 2-CdA. Eight patients (20%) have relapsed at a median of 16 months (range, 3 to 23 months). The remaining 32 patients were observed for a median of 30 months (range, 7 to 43 months). No patients have died. At 3 years, the actuarial disease-free survival rate is 77% (95% confidence interval, 70% to 84%). The median CD4+ lymphocyte count before therapy was 743/microL (range, 58 to 2,201/microL). The median CD4+ nadir after treatment was 139/microL (range, 25 to 580/microL). There was a single opportunistic infection and no second malignancies observed. Although there was evidence of some improvement in CD4+ lymphocyte counts on sequential testing, CD4+ counts remained significantly lower than baseline (P < .0001) at a median of 23 months after therapy (median, 237/microL; range, 25 to 514/microL), and were also lower than baseline (P < .002) in those patients with more than 1 year of follow-up (median, 27 months; range, 13 to 42 months). The median time to reach an absolute CD4+ lymphocyte count of 365/microL, the lower limit of the normal range, was 40 months. Although responses to 2-CdA are durable in the majority of patients with HCL, the uncertain long-term consequences of the observed CD4+ lymphocytopenia suggest caution in the broad application of this therapy.     

The role of complement and gp120-specific antibodies in virus lysis and CD4+ T cell depletion in HIV-1-infected patients

The substantial virus lysis was induced by HIV-1-infected patient serum and normal human complement serum in the presence of purified patient IgG. Non-infected CD4+ T cells coated with the whole virus or with a recombinant HIV-1 envelope gp120 and sensitised with patient IgG were also shown to be susceptible to complement-dependent lysis. The serum level of complement regulatory protein in a fluid phase, the C1-esterase inhibitor, was significantly correlated with serum concentration of C1q-circulating immune complexes (P=0.0062), but inversely with CD4+ T cell count (P < 0.0001). Accordingly, the disease progression in HIV-1-infected patients was significantly correlated with the level of complement activation as determined by serum level of C1-esterase inhibitor (P=0.0001), and inversely correlated with CD4+ cell count (P < 0. 0001) and gp120-specific antibody titre (P=0.0086). These results strongly suggest that the complement activation by gp120-specific antibodies play a very important role in virus clearance, but also in depletion of infected as well as gp120-coated non-infected CD4+ bystander T cells during the course of HIV-1 infection.     

Simple enzyme immunoassay for titration of antibodies to the CD4-binding site of human immunodeficiency virus type 1 gp120

We report the development of an immunoassay for the titration of antibody to the CD4-binding site (CD4BS) of the human immunodeficiency virus type 1 (HIV-1) surface glycoprotein gp120. This assay is a competitive enzyme-linked immunosorbent assay in which serum antibodies compete with labeled F105, a human monoclonal antibody whose corresponding epitope overlaps the conformation-dependent CD4BS, for binding to purified recombinant gp120 coated on a solid phase. Ninety-nine percent (109 of 110) of HIV-1-positive French patients and 91% (51 of 56) of HIV-1-positive African patients had CD4BS antibodies, indicating that the conformational CD4BS epitope is well conserved among different subtypes of HIV-1. Titers of CD4BS antibodies according to clinical status appeared to be not statistically different. A longitudinal study in 21 seroconverters showed that, for the majority of individuals, CD4BS antibodies appeared early and persisted at relatively high titers for several years. None of 21 HIV-2-seropositive patients had CD4BS antibodies in our assay, suggesting that the antibodies produced during HIV-2 infection are not cross-reactive with the CD4BS of HIV-1 gp120.     

Expression of the alpha 5 beta 1 fibronectin receptor on T lymphocytes of patients with HIV-1 infection

AIMS: To evaluate the expression of the alpha 5 beta 1 integrin fibronectin receptor (FNR), which mediates several processes, including phagocytosis, cell motility and the immune response, on T lymphocytes of patients with HIV-1 infection. METHODS: T lymphocytes were incubated with monoclonal antibody directed against FNR and then with monoclonal antibodies, conjugated with phycoerythrin, directed against CD3, CD4 and CD8 positive cells. Expression of FNR on CD3, CD4 and CD8 positive cells was analysed using flow cytometry. RESULTS: Normal expression of FNR was observed on CD3 positive cells from asymptomatic HIV positive patients and those with AIDS. Increased expression of FNR was observed on CD8 positive cells from asymptomatic HIV positive patients and on CD4 positive cells from patients with AIDS. Increased FNR expression was observed on CD4 positive cells from patients with AIDS, particularly those with opportunistic infections caused by Pneumocystis carinii, Mycobacterium sp, Toxoplasma gondii, and Cryptococcus neoformans. CONCLUSION: Increased expression of FNR on CD8 and CD4 positive cells in asymptomatic HIV positive patients and those with AIDS, respectively, may be an epiphenomenon correlated with lymphocyte activation by HIV-1 or opportunistic infection, Further study is required to determine whether upregulation of FNR expression has a direct role in the pathogenesis of AIDS.     

Regression of Kaposi's sarcoma during therapy with HIV-1 protease inhibitors: a prospective pilot study

BACKGROUND: Early studies using HIV protease inhibitors (PI) showed regression of Kaposi's sarcoma (KS) lesions in some patients. OBJECTIVE: Our purpose was to determine prospectively the influence of PI on HIV-related KS. METHODS: KS lesions of nine patients with progressive cutaneous disease were prospectively evaluated clinically and by means of epiluminescence microscopy before and during PI therapy. HIV viremia and CD4 cell count were measured in parallel. RESULTS: All patients experienced reduction or initial stabilization of KS lesions during the first 4 to 8 weeks of HIV-1 PI therapy. After a median follow-up of 7 months and according to AIDS Clinical Trials Groups criteria, six patients had a partial response, two showed stable disease, and in one noncompliant patient KS progressed, requiring chemotherapy. With epiluminescence microscopy, a reduction in skin surface alterations, lesional size, and color intensity was demonstrated in six of nine patients. PI induced a median decrease in viremia of 1.66 log and a median increase in the CD4 count of 49 cells/mm3. CONCLUSION: In this series, HIV PI therapy reduced or stabilized KS. The efficacy of HIV-1 PI in KS may result from the improvement in cellular immunity. These results suggest the use of PI in AIDS-related KS regardless of the level of CD4 lymphocyte count and HIV viremia.     

Dysregulation of membrane-bound tumor necrosis factor-alpha and tumor necrosis factor receptors on mononuclear cells in human immunodeficiency virus type 1 infection: low percentage of p75-tumor necrosis factor receptor positive cells in patients with advanced disease and high viral load

The correlation of persistent tumor necrosis factor-alpha (TNF-alpha) activation with disease progression in patients infected with human immunodeficiency virus type 1 (HIV-1), suggests a role for TNF-alpha in the pathogenesis of HIV-1 infection. In the present study, we examined by flow cytometry the expression of membrane-bound (m) components of the TNF system in 33 HIV-1-infected patients and 12 healthy controls. While peripheral blood mononuclear cells (PBMC) from asymptomatic and symptomatic non-acquired immune deficiency syndrome (AIDS) patients showed a significantly increased percentage of mTNF-alpha+ and mTNF receptor (TNFR)+ cells compared with controls, this was not found in the AIDS group. Compared with healthy controls, AIDS patients had a significantly decreased percentage of both monocytes and lymphocytes expressing p75-TNFR. PBMC from AIDS patients showed a higher p75-TNFR mRNA level and a higher spontaneous release of soluble p75-TNFR than healthy individuals, suggesting enhanced cell surface turnover of this TNFR. The low expression of TNFRs on both lymphocytes and monocytes in the AIDS group was associated with high numbers of HIV-1 RNA copies in plasma, low numbers of CD4+ lymphocytes, and high serum levels of soluble TNFRs. AIDS patients had a decreased percentage of CD8+ lymphocytes expressing TNFRs compared with healthy controls. In contrast, these patients, as well as symptomatic non-AIDS patients, had an increased percentage of TNF-alpha+ and TNFRs+ cells among remaining CD4+ lymphocytes. The pattern of abnormalities seen in AIDS patients suggests a role for persistent activation of the TNF system in the accelerated CD4+ lymphocyte destruction, the enhanced HIV-1 replication, and the markedly impaired antimicrobial defense in advanced HIV-1-related disease.     

Efficacy of zidovudine and human immunodeficiency virus (HIV) hyperimmune immunoglobulin for reducing perinatal HIV transmission from HIV-infected women with advanced disease: results of Pediatric AIDS Clinical Trials Group protocol 185

Pediatric AIDS Clinical Trials Group protocol 185 evaluated whether zidovudine combined with human immunodeficiency virus (HIV) hyperimmune immunoglobulin (HIVIG) infusions administered monthly during pregnancy and to the neonate at birth would significantly lower perinatal HIV transmission compared with treatment with zidovudine and intravenous immunoglobulin (IVIG) without HIV antibody. Subjects had baseline CD4 cell counts /=200/microL) but not with time of zidovudine initiation (5.6% vs. 4.8% if started before vs. during pregnancy; P=. 75). The Kaplan-Meier transmission rate for HIVIG recipients was 4. 1% (95% confidence interval, 1.5%-6.7%) and for IVIG recipients was 6.0% (2.8%-9.1%) (P=.36). The unexpectedly low transmission confirmed that zidovudine prophylaxis is highly effective, even for women with advanced HIV disease and prior zidovudine therapy, although it limited the study's ability to address whether passive immunization diminishes perinatal transmission.     

Factors predicting the diameter of the popliteal artery in healthy humans

A prospective observational study was conducted over a 10-month period to determine the clinical and laboratory manifestations of cryptococcal meningitis in Zimbabwe, a country where antifungal agents are not widely available. Eighty-nine patients with cryptococcal meningitis (median age, 34 years; range, 11-63 years; 56 males) were identified from 406 patients for whom a clinical diagnosis of meningitis had been made. All patients tested were positive for antibody to human immunodeficiency virus. Cryptococcal meningitis was the first AIDS-defining illness in 88% of patients. Typical presentations were headache, mental impairment, and meningism (median duration, 14 days; range, 1-180 days). The median CD4+ cell count was 70/microL (range, 0-651/microL). The cumulative median survival from the time of diagnosis was 14 days (range, 0-233 days); 22% of patients survived for >30 days. Independent indicators of a good prognosis were not identified. This study provides a unique basis for the development of novel management strategies for patients with cryptococcal meningitis who reside in resource-poor countries.     

Similar pharmacological properties of 8-OH-DPAT and alnespirone (S 20499) at dopamine receptors: comparison with buspirone

OBJECTIVE: We investigated whether the induction of antilymphocyte autoantibodies and immune complexes is associated with the activity of HIV replication. METHODS: Viral HIV-1 RNA was measured in the plasma samples of 84 HIV+ hemophilia patients and correlated with the IgM, IgG, IgM/IgG and IgM/IgG/gp120 load of circulating CD4+ lymphocytes, CD4+ and CD8+ cell counts, plasma neopterin levels and in vitro T-cell responses to mitogens and pooled allogeneic stimulator cells. RESULTS: Compared to patients with no immune complexes, on circulating CD4+ lymphocytes, viral load was increased in patients with IgM, IgM/IgG or IgM/IgG/gp120 complexes. Sequential analysis of HIV+ patients showed that peaks of retroviral activity were associated with the subsequent formation of CD4+ lymphocyte-reactive IgM and IgG autoantibodies and gp120-containing immune complexes. CONCLUSION: The induction of autoantibodies and immune complexes attached to CD4+ lymphocytes is associated with periods of increased viral activity in HIV-infected patients.     

Inhibition of bispecific monoclonal antibody (bsAb)-targeted cytolysis by human anti-mouse antibodies in ovarian carcinoma patients treated with bsAb-targeted activated T-lymphocytes

T lymphocytes of 8 patients with ovarian cancer were targeted to the tumor cells using F(ab')2 fragments of a bispecific monoclonal antibody (bsAb), specific for CD3 (a component of the T lymphocyte receptor for antigen) and for the folate receptor MOv18 (overexpressed by ovarian carcinoma cells) as part of a phase I/II study. Phase I (days 0 to 3) consisted of increasing intraperitoneal (i.p.) numbers (10(6)-10(9)) of bsAb-targeted T lymphocytes plus low-dose interleukin-2 (IL-2). Phase II (days 6 to 13, and 27 to 33) consisted of daily i.p. infusions of 10(9) targeted T lymphocytes, 2 mg soluble bsAb, and low-dose IL-2. Using enzyme-linked immunosorbent assays (ELISA), human anti-mouse antibodies (HAMA) were detected in all patients: in the serum from day 13 onwards and in the peritoneal fluid from day 20 onwards. A significant proportion of the HAMA appeared to be directed against the idiotypes of the bsAb specific for CD3 and MOv18, as suggested by (1) the clearly higher ELISA titers against OC/TR bsAb as compared to those against a monoclonal antibody (MAb) with unrelated specificity, and (2) failure to abrogate the capacity of peritoneal fluid containing HAMA to block the binding of OC/TR bsAb to MOv18+ or CD3+ cells by absorption of human anti-mouse IgG-framework antibodies in peritoneal fluid to immobilized mouse IgG. The OC/TR-targeted cytolysis of the MOv18+ ovarian carcinoma cell line Igrov-I by autologous T lymphocytes was inhibited by peritoneal fluid samples containing relatively high HAMA titers. Such inhibitory activity was never detected at the start of phase II, but coincided with the last series of i.p. infusions of targeted T lymphocytes in 2 patients.     

Role of Fas ligand and receptor in the mechanism of T-cell depletion in acquired immunodeficiency syndrome: effect on CD4+ lymphocyte depletion and human immunodeficiency virus replication

Direct killing of CD4+ lymphocytes by human immunodeficiency virus-1 (HIV-1) probably cannot account for the magnitude of the loss of these cells during the course of HIV-1 infection. Experimental evidence supports a pathophysiologic role of the apoptotic process in depletion of CD4 cells in acquired immunodeficiency syndrome (AIDS). The Fas-receptor/Fas-ligand (Fas-R/Fas-L) system mediates signals for apoptosis of susceptible lymphocytes and lympoblastoid cell lines. A number of investigators have recently reported increased expression of the Fas receptor in individuals with HIV infection, along with increased sensitivity of their lymphocytes to anti-Fas antibody mimicking Fas ligand. We attempted to determine the role of Fas-mediated apoptosis in disease progression and viral replication. Increased Fas-receptor (CD95) expression on CD4+ and CD8+ lymphocytes was found in a large group of HIV-1-infected patients compared with normal controls; individuals with a diagnosis of AIDS and a history of opportunistic infection had significantly more Fas receptor expression than did asymptomatic HIV-infected persons and normal blood donor controls (P < .01). Triggering of the Fas-R by agonistic anti-Fas monoclonal antibody, CH11, was preferentially associated with apoptosis in the CD4+ cells; this effect was more pronounced in lymphocytes derived from HIV+ individuals. Soluble and membrane-bound forms of Fas-L were produced in greater amounts in peripheral blood mononuclear cells (PBMC) cultures and in plasma obtained from HIV-1-infected persons than from normal controls. Furthermore, triggering of lymphocytes from HIV-infected persons by CH11 increased levels of interleukin-1beta converting enzyme (ICE), a protein associated with apoptosis. When PBMC were cultured in the presence of CH11, p24 production per number of viable cells was decreased as compared with the same PBMC without CH11 (P < .01). These findings suggest that multiple mechanisms, including increased production of Fas-L by infected PBMC, increased Fas-R expression, and induction of a protease of ICE family, may play roles in the apoptotic depletion of CD4+ cells in HIV infection.     

Pilot trial of infusional cyclophosphamide, doxorubicin, and etoposide plus didanosine and filgrastim in patients with human immunodeficiency virus-associated non-Hodgkin's lymphoma

PURPOSE: To determine the following: (1) the feasibility of combining the antiretroviral didanosine (ddl) with a 96-hour continuous intravenous (IV) infusion of cyclophosphamide (800 mg/m2), doxorubicin (50 mg/m2), and etoposide (240 mg/m2) (CDE) plus filgrastim in patients with non-Hodgkin's lymphoma (NHL) associated with human immunodeficiency virus (HIV) infection; (2) the effect of ddl on CDE-induced myelosuppression and CD4 lymphopenia; and (3) the effect of CDE on serum p24 antigen and quantitative HIV blood cultures. METHODS: Twenty-five patients with HIV-related NHL received CDE every 28 or more days. Consecutive patients were assigned in an alternating fashion to group A (ddl given at a standard dose during cycles one, two, five, and six) or group B (ddl given during cycles three, four, five, and six). RESULTS: ddl use was associated with less leukopenia (mean nadir, 3.33 v 1.49 x 10(3)/microL; p = .03), neutropenia (2.38 v 1.07 x 10(3)/microL; p = .03), and thrombocytopenia (76 v 48 x 10(3)/microL; p = .059), and fewer RBC (1.6 v 3.1 per cycle; p < .01) and platelet transfusions (0.7 v 1.5 per cycle; p < .01), but had no significant effect on CD4 lymphopenia. Furthermore, lymphomatous bone marrow involvement and low CD4 count were associated with significantly greater myelosuppression. Although there was no substantial change in serum p24 antigen, the HIV blood culture became quantitatively more positive or converted from negative to positive in seven patients (64%). Complete response (CR) occurred in 58% of patients (95% confidence interval, 38% to 78%), median CR duration exceeded 18 months, tumor-related mortality was 20%, and median survival was 18.4 months. CONCLUSION: Our results suggest that the CDE and filgrastim regimen is tolerable and effective for patients with HIV-associated NHL, and that combination with ddl is feasible and may result in less myelosuppression.     

Activation of blood T lymphocytes down-regulates CXCR4 expression and interferes with propagation of X4 HIV strains

The chemokine receptor CXCR4 serves as a coreceptor for HIV-1 entry into CD4+ cells, in particular for strains emerging late in the infection. Cell surface expression of CXCR4 has, therefore, important implications for HIV-1 pathogenesis. Using blood lymphocytes cultured under various conditions, we studied the expression and regulation of CXCR4. Flow cytometry showed that only about 20% of freshly isolated lymphocytes expressed CXCR4 on the cell surface whereas in 80% of resting blood lymphocytes CXCR4 was located intracellularly. Within a few hours in culture, the intracellular CXCR4 was translocated to the surface and was expressed in the large majority of both naive and memory lymphocytes. A decrease in surface expression of CXCR4 was found when lymphocytes cultured overnight for maximal receptor expression were stimulated with phytohemagglutinin, anti-CD3 antibodies, phorbol 12-myristate 13-acetate and stromal cell-derived factor-1. The superantigen staphylococcal enterotoxin A, a more selective stimulus, induced a marked decrease in CXCR4 expression preferentially in cells positive for the CD25 activation marker. Confocal laser scanning microscopy demonstrated the presence of CXCR4 in the cytosol and on the surface of resting lymphocytes and also showed CXCR4 redistribution after activation. The number of cells infected by the X4 HIV strain NL4.3 paralleled the expression of CXCR4 in CD4+ T lymphocytes. Sustained reduction of CXCR4 cell surface expression upon activation with phytohemagglutinin correlated with a low number of CD4+ T lymphocytes expressing HIV p24 gag antigen. Our results indicate that activation of CD4+ T lymphocytes reduces surface expression of CXCR4 in part by receptor internalization and that cell activation-dependent CXCR4 down-regulation limits spread of infection by X4 viruses.     

Spectrum of immunodeficiency in HIV-1-infected patients with pulmonary tuberculosis in Zaire

Tuberculosis (TB) is the most common opportunistic infection in African patients who die from AIDS, yet the stage of immunodeficiency at which TB develops is uncertain. We studied the immune status of HIV-infected outpatients with pulmonary TB in relation to their clinical presentation in a cross-sectional study of 216 HIV-seropositive and 146 HIV-seronegative ambulatory incident cases of smear-positive and culture-positive pulmonary TB in Kinshasa, Zaire. HIV-seropositive and seronegative patients had median CD4 lymphocyte counts of 316.5/microL and 830.5/microL, respectively. Of the HIV-seropositive patients, 32.9% had less than 200 CD4 lymphocytes/microL, 37% between 200 and 499, and 30.1% 500 or more. Clinical AIDS, as defined by the WHO clinical case-definition or a modified version, was of similar limited use as a predictor of immunodeficiency. Among HIV-seropositive patients, oral candidosis, lymphopenia, a negative tuberculin purified protein derivative test, and cutaneous anergy were strongly associated with CD4 counts of less than 200/microL, and seemed to be better markers of immune dysfunction. We conclude that pulmonary TB develops across a broad spectrum of HIV-induced immunodeficiency and that a diagnosis of pulmonary TB is of limited use as a marker of stage of HIV disease in African HIV-infected outpatients.     

Association of serum Rituximab (IDEC-C2B8) concentration and anti-tumor response in the treatment of recurrent low-grade or follicular non-Hodgkin's lymphoma

BACKGROUND: Monoclonal antibodies are being utilized for treatment of patients with low-grade non-Hodgkin's lymphoma as well as other cancers. Results from phase I and II clinical studies has shown that the chimeric monoclonal antibody Rituximab has minimal toxicity and significant therapeutic activity in low grade non-Hodgkin's lymphoma. PATIENTS AND METHODS: We have recently reported on a multicentre pivotal phase III clinical trial involving 166 patients with recurrent low-grade lymphoma who were treated with four infusions of Rituximab. Eighty patients (48%) achieved objective responses including 10 patients (6%) with complete responses. Overall, 126 patients (76%) had a > or = 20% reduction in overall tumor size. The median response duration and time to progression are 11.6 and 13.2 months, respectively. The infusional and long term toxicities were limited. RESULTS: In this report we describe the pharmacokinetic data obtained on these patients. Measurable concentrations of Rituximab were detected in all patients after the first infusion and increased throughout the treatment course. The half-life of the monoclonal antibody increased from 76.3 hours after the first infusion to 205.8 hours after the fourth infusion and was concomitant with a four-fold decrease in the antibody clearance. At three months and six months post-treatment, the median Rituximab serum levels were 20.3 micrograms/ml (range 0.0 to 96.8 micrograms/ml in 104 patients) and 1.3 micrograms/ml (range 0.0-28.7 micrograms/ml in 13 patients), respectively. A statistically significant correlation was found between the median antibody concentration and response for multiple time points during the treatment and followup. The mean serum antibody concentration was also inversely correlated with measurements of tumor bulk and with the number of circulating B cells at baseline. CONCLUSIONS: We conclude that Rituximab is therapeutically effective against B-cell lymphoma. Pharmacokinetic data suggests that certain subsets of patients may possibly benefit from increased dosing and studies to address this are currently underway.