CROI 2018 Abstract eBook

Abstract eBook

Poster Abstracts

substantial increase in the proportions of peripheral blood plasmablasts (wk12 p=0.033), which is the precursor of the antibody-secreting plasma cell. In the lymph nodes, we found an increase in proportions of follicular B cells (p=0.016) and the germinal center B cells (p=0.078), the main B cell subsets that reside in primary and secondary B cell follicles. Consistent with these changes toward a more differentiated B cell phenotype we found increased levels of total IgG (p=0.019) as well as subclasses IgG1 (p=0.042), IgG2 (p=0.021), and IgG3 (p=0.002), after 12 wk treatment. Of note, the IgG3 subclass is superior in its binding affinity for Fc-receptors and is known to be particularly effective in the induction of effector functions. Conclusion: Lefitolimod markedly enhanced B cell differentiation in circulating B cells. The increase in plasmablasts is indicative of an enhanced differentiation of activated antibody-secreting plasma cells, which is supported by observed increase in IgG plasma levels. In lymph nodes the increase in follicular and germinal center B cells point towards a restoration of lymph node architecture. Overall, these data suggest improved lymph node function and humoral immune response in HIV+ individuals on ART, when treated with lefitolimod. 316 A BISPECIFIC APPROACH FOR TARGETING NEGATIVE CHECKPOINT RECEPTORS IN HIV-1 LATENCY Debbie S. Ruelas 1 , Yanyan Zheng 1 , Laura Garvin-Queen 1 , Fahimeh Raoufi 1 , Laurence Fayadat-Dilman 1 , Yuan Li 2 , Julie Strizki 2 , Richard Barnard 2 , Steven G. Deeks 3 , Mohammad Tabrizifard 1 , Daniel Gorman 1 1 Merck & Co, Inc, Palo Alto, CA, USA, 2 Merck & Co, Inc, West Point, PA, USA, 3 University of California San Francisco, San Francisco, CA, USA Background: HIV infection is associated with persistent upregulation of PD-1, LAG-3, TIGIT and perhaps other checkpoint molecules, particularly on HIV-specific T cells. We hypothesize that simultaneous engagement of multiple targets via bispecific antibodies (BsAbs) will enhance anti-HIV efficacy compared to single or combination approaches. Methods: Two BsAbs targeting the negative checkpoint receptors PD-1 & LAG-3 and PD-1 & TIGIT, as well as the corresponding monospecific antibodies, were developed. The secretion of 10 pro-inflammatory cytokines by PBMCs from HIV-infected subjects following stimulation with gag peptides in the presence of BsAbs or monospecific antibodies was quantified. Checkpoint receptor expression by HIV-specific CD8 T cells from infected individuals was evaluated. Assays to measure the ability of BsAbs to bind receptors in cis or trans were developed. Imaging flow cytometry combined with FRET was used to compare BsAb and monospecific antibody internalization. Results: We studied PMBCs from 26 HIV-infected individuals (18 treated and 8 untreated). As expected, HIV antigens stimulated the secretion of cytokines (IFNγ, IL-2, and TNFα); this effect was enhanced following BsAb co-treatment in a subset of individuals, with the impact more pronounced in untreated donors. About 1 in 3 of all subjects screened demonstrated increased IFNγ production in response to ex vivo BsAb treatment versus isotype control. IFNγ ex vivo responses were generally higher following BsAb-treatment as compared to monospecific antibody-treatment. As compared to total CD8 T cells, LAG-3 and TIGIT receptors were higher on PD-1-positive HIV-specific CD8 T cells from HIV-infected individuals. BsAbs demonstrated binding in both cis- and trans- orientation and were capable of internalization. Conclusion: Previous studies in cancer and other fields have demonstrated a benefit of targeting multiple antigens simultaneously using BsAbs. Our experiments will inform the use of BsAbs versus a combination of bivalent antibodies for an immune checkpoint-targeting approach to treat HIV infection. In addition, the findings that BsAbs are capable of both cis-binding, trans- binding, and internalization are essential to understanding the therapeutic potential of BsAbs. Together this work provides a greater overall understanding of BsAb function and efficacy for immune checkpoint-targeting approaches in HIV infection. 317 HIV INFECTION OF TARGET CELLS IN PEDIATRIC TONSIL IS INHIBITED BY AN HSP90 INHIBITOR Ria Goswami 1 , Holly A. Heimsath 1 , Riley J. Mangan 1 , Joshua A. Eudailey 1 , Guido Ferrari 2 , Timothy Haystead 2 , Barton F. Haynes 1 , Sallie Permar 1 1 Duke Human Vaccine Institute, Durham, NC, USA, 2 Duke University, Durham, NC, USA Background: HIV-1 transmission via breastfeeding, accounting for ~half of the 150,000 pediatric infections annually, often goes unrecognized for many months leading to high viral loads. Therefore, immediate cART cannot be

expected to achieve rapid viral suppression in these infants, potentiating the need for an additional antiviral strategy. HIV utilizes cellular heat shock protein 90 (Hsp90) for completion of its life cycle and bystander T cell activation. Therefore, we hypothesize that targeting Hsp90 along with cART will achieve rapid virologic control and limit establishment of viral reservoir in infants. In the current study, we aimed to investigate the role of an Hsp90 inhibitor Hs10, in inhibiting replication of HIV-1 in human tonsils, representing an in vitro model of an important viral reservoir of breast milk transmission. Methods: Mononuclear cells, isolated from tonsil tissues of children <10 years of age, were infected with GFP-expressing HIV-1. The frequency and activation of T cell subtypes infected in presence or absence of Hs10 was evaluated using flow cytometry. Results: Tonsillar mononuclear cells were infected by HIV-NLGI (mean: 4.02±1.80%, n=3) and HIV-JRFL (mean: 0.57±0.26%, n=3).The highest frequency of infected cells was represented by the central memory populations. Yet, this population was only 4.59±2.98% of the total infected cells, indicating that different subsets of tonsillar CD4+ cells can be targeted by HIV-1. A dose- response curve for Hs10 demonstrated that 100nM concentration was most effective in inhibiting the frequency of HIV infected of tonsillar cells in vitro (mean inhibition: 65.8±15.91%, n=5), without promoting cell death (mean live cells: 88.58±11.70%, n=5). Addition of Hs10 also resulted in a reduction in early activation of CD4+ T cells (CD25+ CD4+: mean reduction: 68.3±5.4%, n=5). Interestingly, even when the compound was added 24h pi, the proportion of infected T cells was reduced by 68.4% (n=5), demonstrating that this compound can target established infections in lymphoid tissues. Conclusion: Our study demonstrates that inhibition of Hsp90 blocks HIV infection by reducing the number of target cells blocking bystander T cell activation. This study is anticipated to provide compelling data towards the efficacy of combining Hsp90 inhibitors and cART to achieve rapid virologic control, and limit establishment of HIV reservoirs in pediatric populations, which would open the possibility of HIV remission or functional cure in HIV- infected breastfed infants. 318 ALTERED AND INCOMPLETE IMMUNE RECONSTITUTION IN HIV+ STEM CELL TRANSPLANT RECIPIENTS Daniel D. Murray 1 , John Zaunders 1 , Carole Ford 2 , Kersten Koelsch 1 , Samuel T. Milliken 2 , Orla Morrissey 3 , Sharon Avery 4 , Joseph Sasadeusz 5 , Matthew Law 1 , Anthony Kelleher 1 , Sharon R. Lewin 6 , David A. Cooper 1 , John Moore 2 , Mark Polizzotto 1 1 Kirby Institute, Sydney, NSW, Australia, 2 St. Vincent’s Hospital, Sydney, NSW, Australia, 3 Monash University, Melbourne, VIC, Australia, 4 Alfred Hospital, Melbourne, VIC, Australia, 5 Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia, 6 University of Melbourne, Melbourne, VIC, Australia Background: HIV+ individuals are at increased risk of developing the malignancies that require allogeneic stem cell transplants (ASCT). While there is increasing evidence of the safety of ASCT in HIV+ individuals on antiretroviral therapy (ART), there has been little evaluation of the kinetics of immune reconstitution. Methods: We prospectively evaluated HIV and CMV viral loads, and immune reconstitution measured by CD4 and CD8 peripheral T cell counts in six HIV+ individuals on ART undergoing ASCT for haematological malignancies. T cell subsets were compared with HIV-negative ASCT controls (n=17). Four HIV ASCT subjects also consented to fine-needle biopsy (FNB) of inguinal lymph-nodes pre and up to 4 years post-ASCT, and these findings were compared to non-ASCT HIV+ (treated n=11, untreated n=10) and HIV-negative (n=10) controls. Frozen PBMC were available for two subjects and we performed additional detailed flow cytometric characterisation to determine CD4 and CD8 subsets. Results: Characteristics for HIV-ASCT subjects can be found in Table 1. There were no significant differences in CD4 T cell counts between HIV ASCT subjects (median, IQR=367, 188 cells/µl) and controls (484, 444 cells/ µl) at time-points ~6-12 months post-ASCT. In contrast, CD8 T cells trended higher in HIV-ASCT subjects (1693, 1556 cells/ µl) vs controls (748, 922 cells/ µl; p=NS). In two subjects, both with elevated CD8 counts, further characterisation showed that one individual had elevated activated, non-gut homing, terminally differentiated CD8 T cells, while the other predominantly had activated, gut homing CD8 T cells. Comparisons of FNB T cells showed significantly lower CD4 T cells in HIV-ASCT (median, IQR = 3.1x104, 1.5x105 cells), compared to both HIV+ non-ASCT subjects, on ART (2.3x105, 1.9x105 cells) and untreated (5.9x105, 1.1x106 cells) and HIV-negative non-ASCT controls (8.9x105, 9.8 x105 cells).

Poster Abstracts

CROI 2018 111