Differential effects of administration of a human anti-CD4 monoclonal antibody, HM6G, in nonhuman primates

Ibalizumab, a Novel Monoclonal Antibody for the Management of Multidrug-Resistant HIV-1 Infection

Limited antiretrovirals are currently available for the management of multidrug-resistant (MDR) HIV-1 infection. Ibalizumab, a recombinant humanized monoclonal antibody, represents the first novel agent for HIV-1 management in over a decade and is the first monoclonal antibody for the treatment of MDR HIV-1 infection in combination with other forms of antiretroviral therapy in heavily treatment-experienced adults who are failing their current antiretroviral regimen. Ibalizumab demonstrates a novel mechanism of action as a CD4-directed postattachment inhibitor and has a favorable pharmacokinetic profile that allows for a dosing interval of every 14 days after an initial loading dose. Clinical studies have demonstrated reasonably substantial antiretroviral activity with ibalizumab among a complex patient population with advanced HIV-1 infection who are receiving an optimized background regimen, where limited therapeutic options exist. Ibalizumab was well tolerated in clinical trials, and the most common adverse effects included diarrhea, nausea, dizziness, fatigue, pyrexia, and rash. Resistance to ibalizumab has also been observed via reduced expression or loss of the potential N-linked glycosylation sites in the V5 loop of the envelope glycoprotein 120. The mechanism of action, pharmacokinetic parameters, efficacy, and safety of ibalizumab present an advance in the management of MDR HIV-1 infection. Future studies and postmarketing experience will further determine longer-term clinical efficacy, safety, and resistance data for ibalizumab.

Ibalizumab

PURPOSE OF REVIEW

Antiretroviral options for patients infected with multiclass resistant HIV-1 warrant the development of new agents with unique mechanisms of action and modes of delivery. Here we review one such agent, ibalizumab, a parenteral CD4 postattachment inhibitor that has demonstrated efficacy as part of combination antiretroviral therapy in the treatment of HIV-1.

RECENT FINDINGS

In a phase III clinical trial in HIV-infected participants with multiclass antiretroviral drug resistance, the intravenous administration of ibalizumab led to declines in plasma HIV-1 RNA more than 0.5 log in 83% of participants at 1 week. An optimized background antiretroviral regimen was then added, and plasma HIV-1 RNA became less than 50 copies/ml in 43% of participants at 24 weeks. Adverse effects of ibalizumab were uncommon and generally low grade. Ibalizumab was approved by the US Food and Drug Administration on March 16, 2018, under the trade name Trogarzo.

SUMMARY

Ibalizumab has demonstrated both safety and efficacy in the treatment of HIV-1 infection. Its primary use will be in the setting of multidrug resistant virus as part of combination antiretroviral therapy. Further enhancements of ibalizumab to prolong its clearance and broaden its activity are in development.

Monoclonal antibody-induced cytokine-release syndrome

Monoclonal antibodies (mAbs) are widely used in anti-inflammatory and tumor therapy. Although effective, mAbs can cause a variety of adverse effects. An important toxicity seen with a few mAbs is cytokine-release syndrome (CRS). These mAbs include: alemtuzumab, muromonab-CD3, rituximab, tosituzumab, CP-870,893, LO-CD2a/BTI-322 and TGN1412. By contrast, over 30 mAbs used clinically are not associated with CRS. In this review, the clinical aspects of CRS, the mAbs associated with CRS, the cytokines involved and putative mechanisms mediating cytokine release will be discussed. This will be followed by a discussion of the poor predictive value of studies in animals and the prospects for creating in vitro screens. Finally, approaches to decreasing the probability of CRS, decreasing the severity or treating CRS, should it occur, will be described.

Human immunodeficiency virus type 1 escape from cyclotriazadisulfonamide-induced CD4-targeted entry inhibition is associated with increased neutralizing antibody susceptibility

Continuous specific downmodulation of CD4 receptor expression in T lymphocytes by the small molecule cyclotriazadisulfonamide (CADA) selected for the CADA-resistant human immunodeficiency virus type 1 (HIV-1) NL4.3 virus containing unique mutations in the C4 and V5 regions of gp120, likely stabilizing the CD4-binding conformation. The amino acid changes in Env were associated with decreased susceptibility to anti-CD4 monoclonal antibody treatment of the cells and with higher susceptibility of the virus to soluble CD4. In addition, the acquired ability of a CADA-resistant virus to infect cells with low CD4 expression was associated with an increased susceptibility of the virus to neutralizing antibodies from sera of several HIV-1-infected patients.

Novel human antibody therapeutics: the age of the Umabs

Monoclonal antibodies represent a major and increasingly important category of biotechnology products for the treatment of human diseases. The state-of-the-art of antibody technology has evolved to the point where therapeutic monoclonal antibodies, that are practically indistinguishable from antibodies induced in humans, are routinely generated. We depict how our science-based approach can be used to further improve the efficacy of antibody therapeutics, illustrated by the development of three monoclonal antibodies for various cancer indications: zanolimumab (directed against CD4), ofatumumab (directed against CD20) and zalutumumab (directed against epidermal growth factor receptor).

Safety, pharmacokinetics, and antiretroviral activity of multiple doses of ibalizumab (formerly TNX-355), an anti-CD4 monoclonal antibody, in human immunodeficiency virus type 1-infected adults

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.

Human monoclonal antibodies from transgenic mice

Since the 1986 regulatory approval of muromonomab-CD3, a mouse monoclonal antibody (MAb) directed against the T cell CD3epsilon antigen, MAbs have become an increasingly important class of therapeutic compounds in a variety of disease areas ranging from cancer and autoimmune indications to infectious and cardiac diseases. However, the pathway to the present acceptance of therapeutic MAbs within the pharmaceutical industry has not been smooth. A major hurdle for antibody therapeutics has been the inherent immunogenicity of the most readily available MAbs, those derived from rodents. A variety of technologies have been successfully employed to engineer MAbs with reduced immunogenicity. Implementation of these antibody engineering technologies involves in vitro optimization of lead molecules to generate a clinical candidate. An alternative technology, involving the engineering of strains of mice to produce human instead of mouse antibodies, has been emerging and evolving for the past two decades. Now, with the 2006 US regulatory approval of panitumumab, a fully human antibody directed against the epidermal growth factor receptor, transgenic mice expressing human antibody repertoires join chimerization, CDR grafting, and phage display technologies, as a commercially validated antibody drug discovery platform. With dozens of additional transgenic mouse-derived human MAbs now in clinical development, this new drug discovery platform appears to be firmly established within the pharmaceutical industry.

A human CD4 monoclonal antibody for the treatment of T-cell lymphoma combines inhibition of T-cell signaling by a dual mechanism with potent Fc-dependent effector activity

Zanolimumab is a human IgG1 antibody against CD4, which is in clinical development for the treatment of cutaneous and nodal T-cell lymphomas. Here, we report on its mechanisms of action. Zanolimumab was found to inhibit CD4+ T cells by combining signaling inhibition with the induction of Fc-dependent effector mechanisms. First, T-cell receptor (TCR) signal transduction is inhibited by zanolimumab through a fast, dual mechanism, which is activated within minutes. Ligation of CD4 by zanolimumab effectively inhibits early TCR signaling events but, interestingly, activates signaling through the CD4-associated tyrosine kinase p56lck. An uncoupling of p56lck from the TCR by anti-CD4 allows the kinase to transmit direct inhibitory signals via the inhibitory adaptor molecules Dok-1 and SHIP-1. Second, CD4+ T cells are killed by induction of antibody-dependent cell-mediated cytotoxicity, to which CD45RO+ cells are more sensitive than CD45RA+ cells. Finally, zanolimumab induces down-modulation of CD4 from cell surfaces via a slow Fc-dependent mechanism. In conclusion, zanolimumab rapidly inhibits T-cell signaling via a dual mechanism of action combined with potent Fc-dependent lysis of CD4+ T cells and may act long-term by down-regulating CD4.

Relevance, advantages and limitations of animal models used in the development of monoclonal antibodies for cancer treatment

Antibody humanisation through recombinant DNA technology was a key step in allowing monoclonal antibodies (mAbs) to reach the clinic, particularly for the treatment of cancer. As a consequence, they are less adapted to animal studies, although these studies continue to be important tools to study antibody distribution and action at the level of a whole organism. Moreover, preclinical studies in animals are mandatory before the approval of biologics license applications for mAbs by the U.S. Food and Drug Administration (FDA) or European Agency for the Evaluation of Medicinal Products (EMEA). Different parameters should be taken in consideration before starting animal experiments with recombinant mAbs, including antibody cross-reactivity, immunogenicity, pharmacokinetics, and possible interactions with the host immune system. The various interspecies differences are reviewed and discussed in light of the pharmacological properties expected in patients. In doing so, this article aims to provide a critical review of the animal models used in preclinical studies of mAbs for cancer treatment. In particular, their relevance, advantages and limitations will be discussed.

Biologic therapies in rheumatology: lessons learned, future directions

During the past decade biologic therapies such as monoclonal antibodies and fusion proteins have revolutionized the management of rheumatic disease. By targeting key cytokines and immune cells biologics have provided more specific therapeutic interventions with less immunosuppression. Clinical use, however, has revealed that their theoretical simplicity hides a more complex reality. Efficacy, toxicity and even pharmacodynamic effects can deviate from those predicted, as poignantly illustrated by the catastrophic effects witnessed during the first-into-human administration of TGN1412. This review summarizes lessons gleaned from practical experience and discusses how these can inform future discovery and development of new biologic therapies for rheumatology.

Properties of human IgG1s engineered for enhanced binding to the neonatal Fc receptor (FcRn)

We describe here the functional implications of an increase in IgG binding to the neonatal Fc receptor. We have defined in a systematic fashion the relationship between enhanced FcRn binding of a humanized anti-respiratory syncytial virus (RSV) monoclonal antibody (MEDI-524) and the corresponding biological consequences in cynomolgus monkeys. The triple mutation M252Y/S254T/T256E (YTE) was introduced into the Fc portion of MEDI-524. Whereas these substitutions did not affect the ability of MEDI-524 to bind to its cognate antigen and inhibit RSV replication, they resulted in a 10-fold increase in its binding to both cynomolgus monkey and human FcRn at pH 6.0. MEDI-524-YTE was efficiently released from FcRn at pH 7.4 in both cases. We show that MEDI-524-YTE consistently exhibited a nearly 4-fold increase in serum half-life in cynomolgus monkeys when compared with MEDI-524. This constituted the largest half-life improvement described to date for an IgG in a primate. For the first time, we demonstrate that these sustained serum levels resulted in an up to 4-fold increase in lung bioavailability. Importantly, we also establish that our non-human primate model is relevant to human. Finally, we report that the YTE triple substitution provided a means to modulate the antibody-dependent cell-mediated cytotoxicity (ADCC) activity of a humanized IgG1 directed against the human integrin alpha(v)beta3. Therefore, the YTE substitutions allow the simultaneous modulation of serum half-life, tissue distribution and activity of a given human IgG1.

Biological activities on T lymphocytes of a baculovirus-expressed chimeric recombinant IgG1 antibody with specificity for the CDR3-like loop on the D1 domain of the CD4 molecule

A baculovirus-expressed chimeric recombinant IgG1 (rIgG1) antibody, with Cgamma1 and Ckappa human constant domains, was derived from the murine monoclonal antibody (mAb) 13B8.2, which is specific for the CDR3-like loop of the CD4 molecule and which inhibits HIV-1 replication. Chimeric rIgG1 antibody 13B8.2 blocked, in a dose-dependent manner, antigen presentation through inhibition of subsequent IL-2 secretion by stimulated T cells. The one-way mixed lymphocyte reaction was abrogated by previous addition of baculovirus-produced rIgG1 13B8.2 in the T-cell culture. Anti-proliferative activity of rIgG1 was demonstrated on CD3-activated CD4+ T lymphocytes from healthy donors, such effect being associated with reduced IL-2 secretion of activated T cells. On the other hand, no proliferation inhibition was observed on CD4+ T lymphocytes activated with phorbol ester plus ionomycin, suggesting that rIgG1 13B8.2 preferentially acts on a proximal TCR-induced signaling pathway. Treatment of DBA1/J human CD4-transgenic mice with 100 microg of recombinant antibody for three consecutive days led to in vivo recovery of rIgG1 antibody 13B8.2 both coated on murine T lymphocytes and free in mouse serum, without CD4 depletion or down-modulation. These findings predict that the baculovirus-expressed chimeric rIgG1 anti-CD4 antibody 13B8.2 is a promising candidate for immunotherapy.

Human antibodies from transgenic animals

Laboratory mice provide a ready source of diverse, high-affinity and high-specificity monoclonal antibodies (mAbs). However, development of rodent antibodies as therapeutic agents has been impaired by the inherent immunogenicity of these molecules. One technology that has been explored to generate low immunogenicity mAbs for in vivo therapy involves the use of transgenic mice expressing repertoires of human antibody gene sequences. This technology has now been exploited by over a dozen different pharmaceutical and biotechnology companies toward developing new therapeutic mAbs, and currently at least 33 different drugs in clinical testing--including several in pivotal trials--contain variable regions encoded by human sequences from transgenic mice. The emerging data from these trials provide an early glimpse of the safety and efficacy issues for these molecules. Nevertheless, actual product approval, the biggest challenge so far, is required to fully validate this technology as a drug discovery tool. In the future, it may be possible to extend this technology beyond rodents and use transgenic farm animals to directly generate and produce human sequence polyclonal sera.

Antibody discovery: the use of transgenic mice to generate human monoclonal antibodies for therapeutics

Technical advances made in the 1980s and early 1990s resulted in monoclonal antibodies that are now approved for human therapy. Novel transgenic mouse strains provide a powerful technology platform for creating fully human monoclonal antibodies as therapeutics; ten such antibodies have entered clinical trials since 1998 and more are in preclinical testing. Improved transgenic mouse strains provide a powerful technology platform for creating human therapeutics in the future.

A humanized, nondepleting anti-CD4 antibody that blocks virus entry inhibits virus replication in rhesus monkeys chronically infected with simian immunodeficiency virus

Therapeutic approaches that interfere with viral entry hold promise in preventing or treating HIV infection. Hu5A8, a humanized monoclonal antibody against CD4, was previously shown to inhibit HIV and SIV replication in vitro and was safely administered to rhesus monkeys without depleting CD4(+) T cells. This antibody completely suppressed replication of six different SIVmac 251 primary isolates in vitro. Twice weekly administration of 3-mg/kg doses of hu5A8 for 2 to 4 weeks to SIV-infected rhesus monkeys resulted in sustained plasma antibody levels of > or =20 microg/ml during treatment and 5- to 50-fold decreases in plasma viremia, although suppression of viral replication was transient. Two of three treated monkeys developed antibody responses against the administered monoclonal antibody. Loss of antiviral effect was not temporally associated with anti-hu5A8 antibody responses or due to activation of CD4(+) T cells by hu5A8. However, SIV isolated after hu5A8 treatment was approximately 5-fold more resistant to suppression by hu5A8 than SIV isolates obtained from the same monkeys before treatment. The rapid development of resistance may have resulted from SIV variants that infect cells by a CD4-independent mechanism. These results support the overall concept of anti-CD4 monoclonal antibody treatment to suppress AIDS virus replication in vivo while demonstrating important issues as to its clinical feasibility.