Sex differences in vaccine-induced immunity in mice immunized with integrase-defective lentiviral vector delivering the SARS-CoV-2 Spike protein.

INTRODUCTION

Integrase-defective lentiviral vector (IDLV) delivering the optimized SARS-CoV-2 Spike protein induces strong and persistent immunity in mice. Here, we investigate potential sex-dependent differences by comparing female and male mice for germinal center (GC) reactions and Spike-specific immune responses induced by IDLV delivering an optimized SARS-CoV-2 Spike Wuhan-Hu-1 protein (IDLV-S).

METHODS

Female and male BALB/c mice were injected once intramuscularly with either IDLV-S or IDLV-Mock or were left untreated. Blood, lymph nodes and spleens were collected at selected time points for the analysis of immune responses by flow cytometry, FluoroSpot and neutralization assays.

RESULTS

Strong GC activation was detected at 7 days from the immunization in all vaccinated mice, showing a higher percentage of GC B cells in females. Anti-Spike neutralizing antibodies (nAbs) and T cell responses were detected up to 24 weeks from immunization in all IDLV-S immunized mice. NAbs in sera were more persistent in female than in male mice, and vaccinated females also showed a higher cross-neutralization activity against Spikes from variants of concern, reflecting a better quality of the functional immune response. Both IDLV-S immunized groups showed specific T cell responses evaluated as IFNγ/TNFα producing T cells, with a higher response in females.

DISCUSSION: The higher GC reaction in the immunized females can be the trigger for the more persistent and broader nAb response in females compared to males. Our data confirm sex-dependent vaccine-induced immune responses and support the need of appropriate design of vaccine protocols both at the preclinical and clinical levels.