#5264 CELLULAR IMMUNITY ACTIVATION IN RENAL TRANSPLANT RECIPIENTS AFTER VACCINATION WITH TOZINAMERAN: DIFFERENCES BETWEEN RESPONDERS AND NON-RESPONDERS
Authors: Stai Stamatia , Fylaktou Asimina , Kasimatis Efstratios , Xochelli Aliki , Nikolaidou Vasiliki , Lioulios Georgios , Makrovasili Fani , Tsoulfas Georgios , Papagianni Aikaterini , Stangou Maria 
Published: June 2023

Abstract

Background and Aims
Response to vaccination is a complex procedure, resulting from the activation of various immune cell subpopulations and comprising stimulation of several interactive pathways. The aim of our study was to assess the differences in cellular subpopulations between Renal Transplant Recipients (RTRs) classified as “responders” and “non-responders” to vaccination with Tozinameran, against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Method
Our research was a prospective observational study. Our sample consisted of 39 RTRs on stable immunosuppression, who had a negative history of corona virus disease 2019 (COVID-19) infection and had not achieved to develop protective humoral immunity (i.e., had a negative test for neutralizing antibodies -Nab-) three weeks after the 2nd vaccine dose (T0). We attempted to evaluate immune response 48 hours before (T1) and 3 weeks after (T2) the 3rd Tozinameran dose. Patients with serum Nab levels &gt; 0.3AU/ml (calculated with chemiluminescence immunoassay -CLIA-) and/or enzyme-linked immunosorbent spot (ELISpot) values &gt; 30SFC/5 × 105 PBMCs were regarded as responders. Results were subsequently correlated with variations in cellular subpopulation compositions. Concentrations of CD4+, activated CD4+, CD8+, activated CD8+ T-cells, CD3+CD16+CD56+ (Natural Killer T -NKT-), activated NKT cells, CD3-CD16+CD56+ (Natural Killer -NK-) cells, CD19+, CD19+CD27- (Naïve), CD19+IgD+CD27- (Marginal), CD19+CD24+CD38high (Transitional), CD19+CD27+CD38high (Plasmablasts) and CD19+CD27+ (Memory) B cells were measured with flow cytometry at T1 and T2. We compared the results in the “responders” and the “non-responders” group.

Results
The number of responders significantly increased from T1 [17/39, responders: Nab(-) - ELISpot(+)] to T2 [34/39, responders: Nab and/or ELISpot (+)] (x2 = 16.2, p &lt; 0.0001). No difference was observed between responders and non-responders regarding age, renal function, calcineurin inhibitor levels, dialysis and transplantation vintage. Compared to non-responders, responders presented increased concentrations of: activated CD8+ [23.6(29) vs 9.49(10)/μL, p: 0.044], activated NKT [4.77(8) vs 1.73(2)/μL, p: 0.001] and NK cells [198.91(161) vs 104.45(103)/μL, p: 0.024] at T1 and elevated levels of: total B cells [87.63(101) vs 26.86(42)/μL, p: 0.01], marginal [10.03(13) vs 1.12(5.9)/μL, p: 0.045] and memory B-cells [28.31(42) vs 10.57(19)/μL, p: 0.048] at T2 (see table). A significant increase of activated NKT and naïve B-cells from T1 to T2 [310(174) vs 241(200)/μL, p = 0.02 and 56.2(67) vs 1082(834)/μL, p&lt;0.0001, respectively] was evident only in the responders’ group.

Conclusion
As anticipated, responders to vaccination against SARS-CoV-2 exhibited a quite different immune cell activation profile compared to non-responders. Besides, the 3rd Tozinameran vaccine dose substantially improved RTRs’ immune response and induced a prominent stimulation of the B lymphocyte compartment.