Harrison et al.
Tick-borne encephalitis specific lymphocyte response after allogeneic hematopoietic stem cell transplantation predicts humoral immunity after vaccination
Vaccines. 2021; 9(8):908. doi: 10.3390/vaccines9080908

After allogenic hematopoietic stem cell transplantations (HSCT), patients suffer from immunosuppression due to delayed immune reconstitution, sustained immunosuppressive medication, and underlying graft-versus-host disease, and can therefore be considered as especially vulnerable to infectious diseases. Recent data have shown a significant reduction of humoral response to TBE vaccination in allogenic HSCT recipients assessed by neutralization assay four weeks after the second vaccination with an adjuvanted TBE whole virus vaccine (see Snapshot week 34/2020). In a prospective single-center open study (Vienna, Austria), the cellular immune response to TBE vaccination in allogeneic HSCT recipients one year after transplantation was assessed by analyzing lymphocyte proliferative and cytokine response at baseline, and after two and three TBE vaccinations.

A relevant proportion of HSCT patients (59%), of whom the majority had been vaccinated before HSCT, showed TBE-specific lymphocyte proliferation and a significant Th1 and Th2 cytokine response prior revaccination one year after HSCT, whereas none of the unvaccinated healthy control subjects showed such a response. All HSCT patients with a reasonable TBE antibody response after two vaccinations showed a high TBE-specific lymphocyte proliferation at baseline suggesting that the humoral immune response after TBE vaccination was dependent on preexisting TBE-specific T memory cells. Cytokine measurements showed similar results with significant higher amounts of Th1 and Th2 cytokines produced by humoral responders. All patients with sibling donor (9/9), who had been vaccinated before donation of stem cells, showed significant TBE-specific lymphocyte proliferation at baseline, but only one patient with an unrelated donor (1/8). This allows to suggest that preexisting TBE-specific memory cells may have been transferred from post-thymic repertoire of vaccinated sibling donors to HSCT recipients.

The vaccination status of the donor plays a crucial role in transferring immunity against TBE and improving the antibody response in HSCT recipients after vaccination and this will be enabled in a TBE-endemic setting with high vaccination coverage of the population (like in Austria).

Donor immunity against TBE virus represents an advantage for the HSCT recipients, and a booster vaccination could be offered to related donors prior to stem cell donation to improve immunity against TBE virus in HSCT recipients post transplants.

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