B-063 Towards Improving mRNA Vaccine Effectiveness in Immunosuppressed Adults: Elucidating the Mechanisms and Evaluating Potential Improvement Strategies
Authors: Narasimhan M , Kim K , Mahimainathan L , Zhang R , Malladi S , Muthukumar A 
Published: September 2023

Abstract

Background
The success of COVID-19 mRNA vaccines (Co-mV) has provided a renewed impetus in developing “onetime universal flu, COVID”, and other mRNA-based vaccines to offer broader and long-lasting protection. However, to bring this endeavor to fruition, it is of prime importance to address the mechanism(s) underlying poor vaccine response in some patients and close this gap of inequitable effectiveness through improvement strategies, which is the focus of our current study. To date, there is no ‘empirical’ evidence to link the perturbation of translation, a rate-limiting step for mRNA vaccine efficiency, to its dampened response.

Methods
This IRB approved study involved 1) an assessment of a total of 1009 immunocompromised (IC) patients and immunocompetent subjects who had received 2 or more doses of Co-mV, 2) in vitro cell-culture experiments, and 3) in vivo animal studies. Impact of immunosuppressants (ISs), tacrolimus (T), mycophenolate (M), rapamycin/sirolimus (S), and their combinations on Pfizer Co-mV translation were determined by the Spike (Sp) protein expression following Co-mV transfection in HEK293 cells. In vivo impact of ISs on SARS-CoV-2 spike specific antigen (SpAg) and associated antibody levels (IgGSp) in serum were longitudinally assessed (26 days) in Balb/c mice after two doses (2D) of the Pfizer vaccine. Spike Ag and IgGSp levels were assessed in 259 IC patients and 50 healthy controls (HC) who received 2D of Pfizer or Moderna Co-mV. In addition, 67 immunosuppressed solid organ transplant (SOT) patients and 843 non-transplanted (NT) subjects following three doses (3D) of Co-mV were assessed. Expression of Sp and p70S6K phosphorylation (translation surrogate) were evaluated following higher vaccine doses and transient drug holidays. Statistical analysis was performed using GraphPad software 9.3.1. p &lt; 0.05 was considered as statistically significant.

Results
The 2D and 3D Co-mV received IC patients showed a significantly lower IgGSP response (p &lt; 0.0001) relative to their matched controls. M or S profoundly dampened (p &lt; 0.001) the IgGSP response following Co-mV in the IC patients relative to those that were not on these drugs. M and S, when used individually or in combination in HEK293 cells, significantly (p &lt; 0.05) attenuated the Co-mV-induced Sp expression concurrently with translation surrogates. In contrast, T did not change these indices. Notably, the cellular uptake of Co-Mv was not altered by these drugs. In vivo sirolimus combo pretreatment significantly (p &lt; 0.05) attenuated the Co-mV induced IgMSp and IgGSp production. This correlated with a decreasing trend in the early levels (after day 1) of Co-mV-induced Sp immunogen levels. Neither higher Co-mV concentrations (6μg) nor a 1-day break of S could overcome the repressed Sp protein levels. Interestingly, 3-days of S holiday or using T alone rescued Sp levels in vitro.

Conclusion
This is the first study to reveal that ISs, sirolimus and mycophenolate restrain Co-mV-induced Sp protein synthesis via translation suppression. Transient holiday of sirolimus or selective use of tacrolimus at the time of vaccination can be a potential option to rescue translation-dependent Sp protein production. These compelling findings lay a solid foundation for guiding future studies aimed at improving mRNA-based vaccine effectiveness in high-risk IC patients.