Search

Abstract: Ibalizumab, a humanized monoclonal antibody targeting CD4, blocks HIV-1 entry into cells and is the first Food and Drug Adminstration-approved long-acting agent for HIV-1 treatment. In this phase 2a study, 82 HIV-infected adults failing antiretroviral therapy were assigned an individually optimized background regimen (OBR) and randomized 1:1:1 to arm A (15 mg/kg ibalizumab q2wk), arm B (10 mg/kg weekly for 9 weeks, then q2wk), or placebo. Subjects with an inadequate response at week 16 were permitted to cross over to a new OBR plus 15 mg/kg ibalizumab q2wk. At week 16, viral load (VL) reduction was significantly greater than placebo (0.26 log10) in arms A (1.07 log10; P = 0.002) and B (1.33 log10; P < 0.001); CD4+ T cell counts increased significantly in arm A. After week 16, 11/27 (arm B) and 19/27 (placebo) subjects crossed over to OBR plus 15 mg/kg ibalizumab; 8/28 in arm A initiated a new OBR. Ibalizumab treatment resulted in VL reduction at week 24 (-0.77 and -1.19 log10 for arms A and B, respectively, versus -0.32 log10 for placebo) and 48 weeks (-0.54 and -0.77 versus -0.22 log10). Compared with placebo, VL differences were statistically significant for arm B at week 24 (P = 0.001) and week 48 (P = 0.027). CD4+ T cell counts increased significantly by week 48 in both arm A and arm B, relative to placebo. No ibalizumab-related serious adverse events were reported. The durable antiviral activity and tolerability of ibalizumab support its use in treating individuals harboring multidrug-resistant HIV-1., Competing Interests: R.L.H. is a speaker and consultant of Theratechnologies. S.W. is an employee of TaiMed Biologics USA, Inc. S.T.L. was a former employee and shareholder of TaiMed Biologics USA, Inc. during this clinical study. R.B.C. is an employee of Theratechnologies Inc. The remaining authors have no conflicts of interest to disclose., (Copyright © 2021 The Author(s). Published by Wolters Kluwer Health, Inc.)

Ibalizumab (formerly TNX-355) is a first-in-class, monoclonal antibody inhibitor of CD4-mediated human immunodeficiency type 1 (HIV-1) entry. Multiple clinical trials with HIV-infected patients have demonstrated the antiviral activity, safety, and tolerability of ibalizumab treatment. A 9-week phase Ib study adding ibalizumab monotherapy to failing drug regimens led to transient reductions in HIV viral loads and the evolution of HIV-1 variants with reduced susceptibility to ibalizumab. This report characterizes these variants by comparing the phenotypic susceptibilities and envelope (env) sequences of (i) paired baseline and on-treatment virus populations, (ii) individual env clones from selected paired samples, and (iii) env clones containing site-directed mutations. Viruses with reduced susceptibility to ibalizumab were found to exhibit reduced susceptibility to the anti-CD4 antibody RPA-T4. Conversely, susceptibility to soluble CD4, which targets the HIV-1 gp120 envelope protein, was enhanced. No changes in susceptibility to the fusion inhibitor enfuvirtide or the CCR5 antagonist maraviroc were observed. Functionally, viruses with reduced ibalizumab susceptibility also displayed high levels of infectivity relative to those of paired baseline viruses. Individual env clones exhibiting reduced ibalizumab susceptibility contained multiple amino acid changes in different regions relative to the paired baseline clones. In particular, clones with reduced susceptibility to ibalizumab contained fewer potential asparagine-linked glycosylation sites (PNGSs) in variable region 5 (V5) than did paired ibalizumab-susceptible clones. The reduction in ibalizumab susceptibility due to the loss of V5 PNGSs was confirmed by site-directed mutagenesis. Taken together, these findings provide important insights into resistance to this new class of antiretroviral drug.

Ibalizumab (formerly TNX-355) is a humanized monoclonal antibody that binds CD4, the primary receptor for human immunodeficiency virus type 1 (HIV-1), and inhibits the viral entry process. A phase lb multidose study of the safety, pharmacokinetics, and antiviral activity of ibalizumab was conducted with 22 HIV-1-infected patients. Nineteen patients were randomized to receive either 10 mg/kg of body weight weekly (arm A) or a 10-mg/kg loading dose followed by 6 mg/kg every 2 weeks (arm B) intravenously for 9 weeks. Three patients were assigned to receive 25 mg/kg every 2 weeks for five doses (arm C). During the study, the patients remained off other antiretrovirals or continued a stable failing regimen. Treatment with ibalizumab resulted in substantial reductions in HIV-1 RNA levels (0.5 to 1.7 log(10)) in 20 of 22 subjects. In most patients, HIV-1 RNA fell to nadir levels after 1 to 2 weeks of treatment and then returned to baseline despite continued treatment. Baseline viral isolates were susceptible to ibalizumab in vitro, regardless of coreceptor tropism. Emerging resistance to ibalizumab was manifested by reduced maximal percent inhibition in a single-cycle HIV infectivity assay. Resistant isolates remained CD4 dependent and were susceptible to enfuvirtide in vitro. Complete coating of CD4(+) T-cell receptors was correlated with serum ibalizumab concentrations. There was no evidence of CD4(+) T-cell depletion in ibalizumab-treated patients. Ibalizumab was not immunogenic, and no serious drug-related adverse effects occurred. In conclusion, ibalizumab administered either weekly or biweekly was safe and well tolerated and demonstrated antiviral activity. Further studies with ibalizumab in combination with standard antiretroviral treatments are warranted.

Purpose: There were two study questions: How often do HIV-infected patients present with a medical history or concurrent medication use that might contraindicate the use of one or more antiretroviral drugs? What is the frequency of patients having lifestyle behaviors that might preclude them from successfully following an antiretroviral drug regimen?, Method: One hundred patients were given a 52-item questionnaire that asked about their medical histories, concurrent use of non-HAART drugs, and lifestyle. The results were analyzed to determine the frequency of potential side effects, drug interactions, or lifestyle behaviors that could interfere with the patient being able to successfully adhere to antiretroviral drug regimens., Results: 96% of the patients had at least one medical history item or were taking at least one medication that could potentially create a serious side effect to one or more of the 14 antiretroviral drugs that were studied. All of the patients had at least one lifestyle behavior that would have interfered with successful adherence to one or more of the drugs., Conclusion: The questionnaire utilized in the study identified potential factors that could cause medical problems or that could interfere with the successful use of various antiretroviral drugs. The frequency of occurrence of these factors was unexpectedly high.