Regulatory T-Cell Manipulation Is Limited by Anti-Antibody Responses in HIV-1 Env-Immunized RMs

Background:

CD25⁺FoxP3⁺CD4⁺ regulatory T (Treg) cells help mediate antigen tolerance in immune responses. We aimed to dissect the influence of anti-CD25 monoclonal antibody (mAb) on the germinal center response to immunization. We tested three mAb treatment arms: inhibiting CD25⁺ Treg cells (Basiliximab), depleting that population (Anti-Tac), and a control (anti-influenza CH65). We immunized a cohort of rhesus macaques (RMs) with sequential gp120_CH505 Envelopes (Envs) that mimicked the mutational pattern observed during HIV-1 infection and tested for the development of HIV-1 broadly neutralizing antibodies (bnAbs).

Methods:

Nine RMs were randomly divided into three groups that received 1 mg per infusion of Basiliximab, Anti-Tac, or CH65. Plasma antibody responses were assayed by ELISA. Linear epitope mapping of plasma antibodies was performed by peptide microarray. Immune cell phenotypes were evaluated by flow cytometry. Single-cell PCR and sequencing were conducted to define the antibody spectrum of HIV-1 Env-specific memory B cells derived from lymph nodes. IgM anti-IgG in RMs was assayed by ELISA.

Results:

All RMs developed antibodies that blocked CH106 or sCD4 binding to gp120_CH505TF and gp120₆₃₅₂₁. Binding to HIV-1 Env-specific linear epitopes trended lower after each immunization and infusion in RMs that received anti-CD25 treatment, compared to those received CH65. Treg cell and CXCR5-expressing follicular Treg cell frequency was slightly decreased after the first anti-CD25 infusion but was similar after later infusions. Plasma anti-CD25 activity was detectable after the first infusion but limited after later infusions; CH65 infusion did not show the same pattern. We hypothesized that an anti-antibody immune response developed in anti-CD25 infused RMs; these RMs developed rheumatoid factor after anti-CD25 mAb infusion that matched loss of anti-CD25 plasma activity. Notably, the transient Treg cell disruption that we observed was associated with a change in germinal center responses, as assessed by the size and number of vaccine-elicited B-cell clonal lineages in lymphoid tissue.

Conclusions:

Transient Treg perturbation strategies to break immune tolerance and increase poly-reactive anti-Env antibodies in immunized RMs were limited by anti-antibody responses, indicating that immune manipulation strategies to drive the development of protective bnAbs may have off target effects.