P1319: t and b lymphocytes subsets after bnt162b2 anti-sars-cov-2 m-rna vaccination: a comparison between hematopoietic stem cell transplantation patients and healthy controls.

Background: We previously demonstrated that 76% of allogeneic (ALLO) and 94% of autologous (AUTO) hematopoietic stem cell transplantation (HSCT) recipients develop a serological response after two doses of BNT162b2 anti SARS-Cov-2 mRNA vaccine (Attolico et al, BJH 2021). However, less is known about the lymphocyte (Ly) immune profile as possible predictor of response to the vaccine in these immunocompromised patients. Aims: Aim of the study was to evaluate absolute count and maturation profile of T and B Ly subsets in transplanted patients and to compare them to healthy controls (HC). Methods: We evaluated 39 transplanted patients (24 M, 15F; median age: 55 years, range 26-71; 20 AUTO, 19 ALLO) and 78 age and sex matched HC, after completion of the vaccination program. Samples were collected one month after the second and the third dose. Eight out of 39 patients (21%) did not respond to vaccination (NR: anti Spike titer<50 AU/ml): 6 ALLO, 2 AUTO. Responders (R: ≥50 AU/ml) were 31 (79%). T, B and NK Ly counts were performed with Multitest 6-color TBNK reagent, using FACSCanto cytofluorimeter and Canto software (Becton Dickinson). B and T cell maturation was evaluated with DuraClone IM B and T cells kits, using Navios cytofluorimeter and Kaluza software (Beckman Coulter). Comparison between groups was performed using the Mann-Whitney and Kruskall Wallis tests. Results: No differences were observed in total Ly count between all patients and HC (Fig.1A). However, the analysis of Ly subsets revealed that HC had significantly higher CD4+ count; by contrast, R exhibited higher CD8+, CD16/56+ and CD19+ counts (Fig.1B). When comparing HC to AUTO and ALLO subgroups, we observed that only AUTO patients had a significantly lower CD4 count (p 0.0006). CD4/CD8 Ratio was higher in HC than in both R and NR patients (Fig.1C). We compared Ly subsets before and after the completion of the two doses of vaccination schedule: interestingly, after the second dose, R exhibited significantly higher total Ly counts, CD3+, CD4+ and CD19+ (Fig.1I). We also evaluated T and B maturation subsets. HC had significantly higher Marginal Zone (MZ), unswitched memory and transitional B cells, while R had higher B naïve counts (Fig.1D). The comparison of T CD4+ maturation pattern showed that HC had significantly higher central memory, naïve counts and exhaust CD279+ counts, while R had higher effector memory, senescent CD57+ and senescent CD27-.(Fig.1E) When analyzing the T CD8+ maturation subsets, we found that HC had significantly higher central memory, naïve and exhaust CD279+ while patients had higher effector memory, effector T, senescent CD57+ and CD27-.(Fig.1F) No differences were observed between AUTO and ALLO patients regarding B and T maturation patterns. Despite booster dose recovered, in terms of antibody titer, all the 8 NR after the first two doses, we did not notice any difference when comparing Ly subsets before and one month after the third dose (Fig.1G). Likewise, no differences were shown in Ly subsets of R before and one month after the third dose (Fig.1H). Image:Summary/Conclusion: Overall, our preliminary evaluations show differences in Ly subsets amounts and T and B maturation profiles between HC and transplant patients. Furthermore, no changes were observed before and after the booster dose even in NR who subsequently developed an antibody response. Finally, our study confirms the predictive role of CD4+/CD8+ ratio for the response to vaccination.