CROI 2025 Abstract eBook

Abstract eBook

Poster Abstracts

434

Improved Immunogenicity of a VLP-Forming mRNA Vaccine for HIV-1 Mamta Singh National Institutes of Health, Bethesda, MD, USA Background: The HIV-1 envelope (Env) is the sole target of broadly neutralizing antibodies and, therefore, the context in which it is presented to the immune system is critical for efficiently engaging responder B cells. We previously designed and tested in pre-clinical models a virus-like particle (VLP)-forming env-gag mRNA vaccine that elicited tier-2 neutralizing antibodies and protection against heterologous SHIV infection in rhesus macaques. Here, we further optimize this platform by inclusion of the viral protease to process Gag and produce mature, rather than immature, VLPs. We hypothesized that protease supplementation could impart mobility to membrane-anchored Env spikes, resulting in Env clustering and subsequent B-cell receptor (BCR) crosslinking. Methods: Appropriately dosed and timed expression of the protease was achieved using a full-length gag-pol mRNA transcript. Mice immunizations were performed to investigate the immunogenicity of the improved vaccine platform. To elucidate the mechanisms underlying the increased effectiveness of protease-containing vaccine platform, we used cryo-electron tomography (cryo-ET) to visualize the structure and organization of Env spikes on the surface of mature and immature virus like particles (VLPs). Results: We found that mRNA formulations both with and without the protease produce VLPs with high density of Env trimers on their surface. Immunization of mice with HIV-1 env mRNA in combination with SIV gag and gag-pol mRNAs induced higher titers of trimer-binding and neutralizing antibodies than env alone or env + gag mRNAs. By cryo-ET, immature VLPs featured a well-organized, assembled Gag lattice underneath the viral membrane and displayed infrequent Env spikes on their surface, which did not show clustering. In contrast, in mature VLPs an organized Gag lattice was not observed, while some particles showed initial core condensation; mature VLPs displayed a higher density of Env spikes, with apparent clustering of 3-4 spikes visible on some particles. Conclusions: Clustering of Env spikes on the surface of mature SHIV gag VLPs may have enhanced BCR crosslinking and, thereby, imparted superior immunogenicity to our gag-pol supplemented VLP-forming mRNA vaccine. These results suggest that vaccines capable of generating mature VLPs may have an enhanced effectiveness. An AI-Redesigned Contemporary HIV-1 Env Consensus Antigen Is More Immunogenic Than a Native Sequence Eric Lewitus 1 , Hongjun Bai 2 , Thujitha Thuraisamy 2 , Bonnie Slike 2 , Michelle Zemil 3 , Tanya Krubit 2 , Diane Bolton 2 , Gordon Joyce 2 , Shelly Krebs 1 , Victoria Polonis 1 , Mangala Rao 2 , Mohamad-Gabriel Alameh 4 , Julie Ake 2 , Sandhya Vasan 3 , Morgane Rolland 1 1 US Military HIV Research Program, 2 United States Military HIV Research Program, Bethesda, MD, USA, 3 Henry M Jackson Foundation, Bethesda, MD, USA, 4 University of Pennsylvania, Philadelphia, PA, USA Background: There is a need to design novel HIV-1 vaccine candidates that could elicit broadly neutralizing antibodies (bnAbs) and that reflect currently circulating viruses. Here we tested a subtype B envelope (Env) consensus designed in silico with shortened hypervariable loops and a native B Env to compare their Ab binding and neutralizing responses in rabbits. Methods: A subtype B Env consensus sequence was derived from circulating viruses sampled since 2011. Env hypervariable loops were modeled using AlphaFold2. HIV-1 env sequences were designed as membrane-bound stabilized trimers and expressed as mRNA encapsulated in lipid nanoparticles (mRNA/ LNP). Rabbits were immunized at weeks 0, 4 and 8 with 20ug of mRNA/LNP encoding either a consensus or a native env (n=8/arm) and blood was collected every other week until week 12. Binding Abs were measured with a multiplex Luminex assay (using fold-change over baseline) and neutralization with a TZM-bl assay using tier 1 (n=5) and 2 (n=12) pseudoviruses. Results: AI-models were used to compare different designs for the hypervariable loops V1, V2, V4 and V5 of the subtype B consensus Env. Modified loops were created to promote Ab accessibility, including by shortening V1, V2 and V5. A native subtype B sequence was selected because it was the Env most sensitive to bnAb neutralization among 32 persons living with HIV-1 in early infection. mRNA transfection showed that both proteins were well expressed as transmembrane proteins and recognized by bnAbs targeting sites of vulnerability. The contemporary consensus B Env induced higher Ab binding responses than the native Env vaccine (average fold change against 10

heterologous Env-gp120s=1579.2 vs 917.2, p<0.001). Rabbits immunized with the consensus elicited broader and more potent neutralizing responses than those who received the native Env after the second or third immunization. At week 10, 3-4 rabbits in the consensus B vaccine group compared to 1-2 rabbits in the native Env group neutralized the 4 Tier 1 strains. Neutralization titers tended to be higher in the group that received the consensus B Env (p=0.081 against MN3; p=0.041 against SF162). Similar results were obtained when comparing consensus and native subtype C sequences. Conclusions: Contemporary HIV-1 Env that are redesigned and optimized with AI tools are well expressed and immunogenic. They elicited superior antibody responses than native Env, warranting further testing as vaccine candidates. Incidence and Predictors of STIs and Effect on Immune Activation in the HVTN 705/HPX2008 Trial Mitch M. Matoga 1 , Jin J. Kee 2 , Michal Juraska 2 , Susan Buchbinder 3 , Nigel Garrett 4 , Frank Tomaka 5 , Wouter Willem 5 , Alison C. Roxby 6 , Huub Gelderblom 2 , Lynda Stranix-Chibanda 7 , Mina Hosseinipour 1 , Ludo Lavreys 8 , M. Juliana McElrath 2 , Linda-Gail Bekker 9 , Glenda Gray 10 , for the HVTN705/HPX2008 Research Group 1 University of North Carolina Project–Malawi, Lilongwe, Malawi, 2 Fred Hutchinson Cancer Center, Seattle, WA, USA, 3 San Francisco Department of Public Health, San Francisco, CA, USA, 4 Centre for the AIDS Programme of Research in South Africa, Durban, South Africa, 5 Janssen Pharmaceuticals, Raritan, NJ, USA, 6 University of Washington, Seattle, WA, USA, 7 University of Zimbabwe Clinical Trials Research Centre, Harare, Zimbabwe, 8 Janssen Infectious Diseases & Vaccines, Beerse, Belgium, 9 Desmond Tutu HIV Foundation, Cape Town, South Africa, 10 South African Medical Research Council, Cape Town, South Africa Background: STIs are common among participants participating in HIV vaccine trials. STIs may lead to proliferated immune responses, which could affect immune responses induced by HIV vaccines. Methods: We conducted a secondary analysis of HVTN 705/HPX2008, a phase 2b placebo-controlled efficacy trial of Ad26.Mos4.HIV and aluminum phosphate-adjuvanted clade C gp140 in preventing HIV-1 infection in cisgender women aged 18 to 35 in Malawi, Mozambique, South Africa, Zambia and Zimbabwe. We calculated the baseline prevalence and incidence of the first occurrence of gonorrhea, chlamydia, trichomoniasis and syphilis or any STI between enrolment and 36 months and explored predictors of incident STIs using a multivariate Cox proportional hazards model. Baseline immune activation markers (T-cell, NK/ILC and DC panels) were compared among participants with and without baseline chlamydia infection by calculating weighted geometric mean ratios (GMR). Results: In the MITT cohort of 2630 women, 841 (32.0%) had an STI at baseline. Of these, median age was 22 years (range: 18, 35) and most (82.4%) had secondary education. In the month prior, the median number of sexual partners was 2 (range: 0, 600) and sexual acts was 8 (range: 0, 800), with minimal (10.0%) consistent condom use. About half (47.8%) of participants exchanged sex for money/gifts and used alcohol during unprotected sex (43.2%) but most (94.1%) reported no prior STI. The incidence of any STI was 27.5% (95% CI: 25.7, 29.4) [chlamydia 17.4% (95% CI: 16.2, 18.7), gonorrhea 9.0% (95% CI: 8.2, 9.8), trichomoniasis 6.7% (95% CI: 6.1, 7.4), and syphilis 1.8% (95% CI: 1.5, 2.2)]. The cumulative incidence of any STI was 52.7% (95% CI: 50.3%, 55.0%) over 36 months. Lower risk of incident STIs was associated with increasing age (hazard ratio (HR): 0.92, 95% CI: 0.90, 0.94) and higher likelihood was associated with recent anal sex (HR: 1.54, 95% CI: 1.07, 2.21) and prior STI (HR: 1.65, 95% CI: 1.16, 2.35). No differences were observed in weighted GMR for a battery of baseline immune markers from women with and without baseline chlamydia except for CD123+ pDCs (weighted GMR = 1.23, 95% CI: 1.06, 1.43). Conclusions: STIs were common among participants in HVTN 705/HPX2008. Risk of incident STIs was higher among women with recent anal sex or prior STI. Generally, Chlamydia infection does not appear to result in differences in baseline immune activation and should not alter immune responses to vaccination. 3-Step Heterologous Immunization Schema Results in Development of Cross-Neutralizing VRC01-Class Abs Parul Agrawal 1 , Kelsey Salladay 1 , Arineh Khechaduri 1 , Julianna A. Rose 1 , Latha Kallur Siddaramaiah 1 , Todd Reese 1 , Xiaoying Shen 2 , David Montefiori 2 , Michael S. Seaman 3 , Marie Pancera 1 , Leonidas Stamatatos 1 1 Fred Hutchinson Cancer Center, Seattle, WA, USA, 2 Duke University, Durham, NC, USA, 3 Beth Israel Deaconess Medical Center, Boston, MA, USA Background: HIV continues to be a major global public health issue with ~39.9 million people living with it at the end of 2023 (WHO). An effective vaccine is

436

Poster Abstracts

435

437

CROI 2025 105