CROI 2019 Abstract eBook

Abstract eBook

Poster Abstracts

356 GS-9722: FIRST-IN-CLASS EFFECTOR-ENHANCED BROADLY NEUTRALIZING ANTIBODY FOR HIV CURE Nathan D. Thomsen , Mini Balakrishnan, Craig S. Pace, Xue Zhang, Magdeleine Hung, Mark R. Nagel, Brian A. Carr, Eric Hu, Helen Yu, George Stepan, Joshua Goldsmith, Bing Xia, Debi Jin, John A. Corbin, Romas Geleziunas Gilead Sciences, Inc, Foster City, CA, USA Background: Select broadly neutralizing anti-HIV antibodies (bNAbs) are capable of simultaneously engaging gp120/gp41 on the surface of infected CD4+ T-cells, and Fc-gamma receptors (FcγRs) on the surface of innate immune effector cells. Such bNAbs can kill HIV infected cells and may thus be capable of reducing or eliminating the HIV reservoir. PGT121 is a particularly promising bNAb in this class, having demonstrated potent in-vitro cell killing as well as in-vivo efficacy in SHIV infected monkeys (Borducchi et al. Nature, in press). Here we describe GS-9722, an engineered variant of PGT121 with enhanced effector function and improved drug-like-properties. Methods: A panel of PGT121 crystallizable-fragment (Fc) mutations was tested in Fc-receptor (FcR) binding assays, primary cell killing assays and preclinical PK studies in order to optimize effector function and PK properties. In parallel with these efforts, in-silico and in-vitro approaches were used to guide the selection of PGT121 antibody binding fragment (Fab) mutations that reduced immunogenic risk and improved drug-like-properties. Results: The Fc engineering campaign identified mutations that enhanced binding to activating FcγRs as well as the neonatal Fc-receptor (FcRn). The resulting antibody demonstrated significantly enhanced killing of HIV infected CD4+ T-cells by primary natural killer (NK) cells isolated frommultiple human donors (mean values: Emax=71%, EC50=0.23 μg/mL) compared to PGT121 (mean values: Emax=11%, EC50=3.4 μg/mL). The Fab engineering campaign identified mutations that removed immunogenic T-cell epitopes, removed glycosylation motifs and improved thermodynamic stability. The Fab mutations had minimal impact on neutralization breadth or potency when tested on a panel of clade B patient isolates (60% at IC95≤15 µg/mL, median IC95=0.18 µg/ mL,) compared to PGT121 (58% at IC95≤15 µg/mL, median IC95=0.33 µg/mL). GS-9722 incorporates all mutations identified in the Fc and Fab engineering campaigns and exhibits a pharmacokinetic profile similar to PGT121 in non- human primate studies. Conclusion: GS-9722 is a first in class effector-enhanced bNAb for the targeted elimination of HIV infected cells and is currently in Ph1b clinical testing. Future studies will explore GS-9722 in combination with additional effector enhanced bNAbs, immune-modulatory agents (i.e. GS-9620), latency reversal agents and therapeutic vaccines in a multi-pronged approach to reduce or eliminate the HIV reservoir. 357 PASSIVE INFUSION OF FC-MODIFIED NAB DOES NOT AFFECT DYNAMICS OF PLASMA VIRUS DECAY Mangaiarkarasi Asokan 1 , Anna Maximova 1 , Joana Dias 1 , Andrew Crowley 2 , Amarendra Pegu 1 , Krisha McKee 1 , Wei Shi 1 , John-Paul Todd 1 , Margaret Ackerman 2 , Lucio Gama 1 , Brandon F. Keele 3 , Jeffrey Lifson 3 , Alan S. Perelson 4 , John R. Mascola 1 , Richard A. Koup 1 1 Vaccine Research Center, NIAID, Bethesda, MD, USA, 2 Dartmouth College, Hanover, NH, USA, 3 AIDS and Cancer Virus Program, Frederick, MD, USA, 4 Los Alamos National Laboratory, Los Alamos, NM, USA Background: Passive bNAb infusion leads to a reduction of HIV plasma viremia in infected people as well as in SHIV-infected rhesus macaques. Potential mechanisms of viral reduction include neutralization of free virus as well as Fc- dependent effector functions that can clear infected cells. Prior mathematical modeling of plasma virus decline during ART treatment can be applied to passive bNAb therapy to delineate the potential mechanism(s) of action. Methods: We generated several Fc-variants of the human IgG1 NAb VRC07- 523 and characterized them for neutralization, complement binding, ADCC, phagocytosis, and binding to rhesus FcgR and FcRn. All variants contained a two amino acid mutation termed LS, that increased affinity for FcRn. Based on these assays, we down selected two variants - LS-LALA and LS-DEL, that showed knock-out or increase in ADCC and phagocytosis respectively, with complement binding knocked out in both. These mAbs were administered at a single dose of 20 mg/kg i.v. to rhesus macaques chronically infected with SHIV-SF162P3 for 6 weeks (n=10 per group). Animals were followed for rate of plasma virus decay, antibody PK (serum and cell-bound) and viral rebound. Results: LS-LALA and LS-DEL groups were similar in the following characteristics - 1) plasma virus decay was delayed for 24h after mAb infusion

peptides or peptides representing only conserved viral epitopes. Four to six weeks post humanization, mice were simultaneously infected with JR-CSF and treated with autologous HSTs. Weekly blood samples were analyzed by flow cytometry to measure changes in the human CD4+/CD8+ levels as well as qRT-PCR to measure viral load. Plasma RNA was subsequently sequenced for the presence of viral escape mutations. Results: Mice engrafted with only the memory CD4+ T-cell subset survived significantly longer than mice engrafted with total CD4+ T-cells and were able to support robust HIV infection sustained out to 20 weeks post engraftment. Daily ARV injections resulted in viral suppression and CD4+ T-cell reconstitution, followed by viral rebound and CD4+ T-cell loss upon ARV cessation. Mice that received autologous HSTs saw significant, transient decreases in plasma viral load compared to the No Treatment group (p<0.0001). Sequencing analysis of plasma virus revealed a dominant escape mutation in one mouse in the HST group suggesting immunological pressure. Early results from an additional in vivo experiment demonstrated similar, significant decreases in viral loads with 66% of mice receiving HST therapy reaching an undetectable viral load 4 weeks post therapy initiation. Conclusion: We have demonstrated that our novel memory CD4+ T-cell humanized mouse model accurately recapitulates many aspects of natural HIV infection while significantly reducing the effects of GvHD. Using this model, we have observed significant decreases in viral load in mice receiving clinically relevant HST products. This platform provides opportunities to assess a variety of immunotherapeutic strategies as well as immunomodulatory approaches in an in vivo, autologous target/effector setting. 355 DIFFERENTIAL EFFECTS OF IL-15 TREATMENT DELIVERED BY DIFFERENT ROUTES IN MACAQUES Antonio Valentin, Dionysios C. Watson, Hrishikesh Pandit, Cristina Bergamaschi, Santhi Devasundaram, Sotirios Fortis, Barbara K. Felber, George N. Pavlakis National Cancer Institute, Frederick, MD, USA Background: Heterodimeric interleukin-15 (hetIL-15) is a native stable form of the cytokine that activates and expands cytotoxic T and NK cells. We have reported that hetIL-15 treatment delivered subcutaneously in SHIV infected macaques results in significant decrease in viral RNA within peripheral lymph nodes (LN) and plasma viral loads. In this study, we have expanded the analysis of the hetIL-15 effects on virus-specific CD8+ T cells, as well as the general lymphocyte population, in immunized MamuA01+ rhesus macaques treated with hetIL-15 subcutaneously (sc), intraperitoneally (ip), intravenously (iv) and intramuscularly (im). Methods: Eight DNA-immunized rhesus macaques received injections of hetIL-15 over 2 weeks using increasing doses of cytokine (step-dosing) by four different routes (sc, ip, iv and im). At the end of the treatment, hetIL-15 effects on different lymphocyte populations were monitored by multi-parametric flow cytometry. Results: All four protocols resulted in systemic expansion of CD8+ T lymphocytes and NK cells with higher granzyme B content. These cells were found in both effector sites, such as liver, vagina and rectum, and secondary lymphoid tissues. A significant increase in cytotoxic effector memory CD8+ T cells was found in lymph nodes from all hetIL-15-treated macaques. CM9 tetramer staining demonstrated that the increase of CD8+ effector T cells in lymphoid organs included actively proliferating SIV-specific T cells with higher granzyme content. Some effects of hetIL-15 treatment were restricted to the specific delivery route. Macaques treated ip showed the highest levels of proliferation in CD8+ lymphocytes obtained from the gastrointestinal tract (duodenum, jejunum, ileum and colon), although the proliferating T cells from the gut did not show any increase in granzyme content. Conclusion: Step-dose administration of hetIL-15 by four different routes is well-tolerated and results in systemic activation and expansion of virus-specific cytotoxic leukocytes that infiltrate LN and peripheral effector sites. The differences observed between LN and the gastrointestinal tract suggest that tissue-specific homeostatic mechanisms may modulate the response of the tissue-resident lymphocytes to hetIL-15. These results suggest that hetIL-15 could be useful in promoting the entry of cytotoxic T cells into areas of chronic HIV replication and contributing to a functional cure of the infection.

Poster Abstracts

CROI 2019 129

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