ABSTRACT
Background: Recent studies have shown that several frequent apheresis platelet donors (more than 20 donations/year for several years) have CD4+ T cell counts below the normal limit (<400 cells/μl) while the levels of other blood cell types (including B cells) remain normal. This lymphopenia does not appear to be associated with an increased susceptibility to infections and cancers, suggesting that it does not affect immune function of the platelet donors with low CD4+ T cell counts. Aims: To assess the immune capacity of apheresis platelet donors with lymphopenia by taking advantage of the recent SARS-CoV-2 vaccination campaign. Methods: Forty-three apheresis platelet donors who donate at least five times per year were recruited. At least half of these participants were frequent donors and were thus more likely to have low CD4+ T cell counts. Their baseline CD4+ T cell count was determined by flow cytometry. The levels of antibodies targeting the SARS-CoV-2 Spike receptor binding domain (RBD) were measured by ELISA before and after vaccination. The level of antibodies against native full-length Spike was determined by flow cytometry using transfected cells expressing different Spike variants of concern (D614G, Delta, Omicron). The avidity of RBD antibodies produced after the first and second dose of vaccine was determined using a modified ELISA in which a chaotropic agent (urea 8 M) was added. The functional properties of vaccine-elicited SARSCoV- 2 antibodies were measured using ADCC and neutralization assays. Results: Of the 43 participants, 27 had pre-vaccination CD4+ T cell counts below 400 cells/μl (low CD4 group) and 16 participants had CD4+ T cell counts in the normal range (400-1600 CD4/μl;normal CD4 group). The levels of RBD-binding antibody did not significantly differ between the low and normal CD4 groups for all three isotypes (IgG, IgA and IgM) after the first and second doses of vaccine. As expected given the maturation of immune response, the avidity of RBD-binding antibodies present in the plasma collected after the second dose of vaccine was significantly higher than that measured in plasma recovered after the first dose. However, the increase was of similar magnitude in both CD4 groups. Recognition of the three Spike variants, as measured by flow cytometry, did not differ significantly between the low and normal CD4 groups. Finally, the antibody(Fc)- mediated effector function (measured by ADCC using cells expressing the wild type Spike) and neutralization capacity of the three variants of concern were comparable for the two groups, after receiving two vaccine doses. Summary/Conclusions: Our data show that low CD4+ T cell counts in apheresis platelet donors do not impair their response to antigenic challenge such as COVID-19 vaccination. This finding is consistent with the previously lack of increased susceptibility of platelet donors with lymphopenia to infections and cancers. Work remains to be done to understand the physiological mechanism behind the low number of CD4+ T cells in the peripheral blood of several plateletpheresis donors.
ABSTRACT
Introduction: About 20% of the Indian population has been vaccinated till September, since its first roll out on 16 January 2021.Majority of Indian population was vaccinated through ChAdOx1nCoV-19 Corona Virus Vaccine (Recombinant), commonly known asCovishield. Although the vaccine is proven safe but occasional reports of Vaccine-induced thrombocytopenia and thrombosis raisedfew eyebrows regarding the safety. Apheresis-derived platelet concentrates are frequently required in all sorts of clinical illnesses andpost-vaccination decrement of platelet counts might lead to increaseddeferral of the plateletpheresis donors.Aims &Objectives: The study aims to find out the effect of Covishield vaccination on deferral rates of plateletpheresis donors. Theprimary objective is to compare deferral rates of vaccinated plateletdonors (cases) from non-vaccinated ones (control) and the secondaryobjective is to correlate vaccination with pre-donation platelet countsof the donors.Materials &Methods: A blood sample was collected from thepotential platelet donors after the standard questionnaire for a complete blood count. Data collected were tabulated in an MS Excelspreadsheet and was analyzed with SPSS v23, p-value ≥ 0.05 wastaken as significant. We compared this data with an equal number ofage and sex-matched platelet donors (controls) from the year 2019.Result: The mean age of cases and controls was 29.69 ± 8.57 and30.15 ± 7.11 respectively. There is a marked difference betweenplatelet counts of cases (188,496.35 ± 72,065.66/mm3) and controls(269,524.50 ± 53,981.60/mm3) with p-value of <0 > 3 than thosewho received 2 doses 179,970.83 ± 66,773.73/mm3. The differencein deferral rates was remarkable between the two groups 34.7% vs0.9% with p-value <0.001. Weak positive correlation is establishedbetween days after 2nd dose and platelet count (rho = 0.2, p = 0.002).Conclusions: Vaccination undoubtedly increased the deferral rates ofplateletpheresis donors due to low platelet counts. Average plateletcounts were low in fully vaccinated individuals, however, plateletreturned to normal counts as the days progress post-vaccination.