Introduction: The infection and/or reactivation of latent CMV and CMV-disease in kidney transplant patients (KTR) increasing the allo-sensitization risk and limiting the possibilities of getting a new transplant. Cellular response is thought to be the responsible of CMV-immunity. However, it is still unknown if T follicular helper cells (TFH), that are specialized in assisting B cell differentiation towards antibody-producing-plasma cells, may contribute to protection through promoting neutralizing antibodies (Nabs). TFH are also known for secreting IL-21, which has been seen to strengthen NK and CD8+ cytolytic activity. TFH cells, mainly found in secondary lymphoid structures, have been identified and named in peripheral blood as circulatory TFH (cTFH). Therefore, the aim of this study is to determine if cTFH could be related to protection against CMV in KTR post-transplantation (Tx).
Methods: From an initial cohort of 227 KTR, patients who received anti-CMV prophylaxis and/or thymoglobulin as induction were excluded. The final group of analysed patients were n=74 and included seropositive recipients transplanted with a CMV+ or CMV- donor. Peripheral blood mononuclear cells (PBMCs) were collected pre- and post-Tx. cTFH were identified as CD4+CXCR5+CCR7loPD1hi by means of flow cytometry. Viral replication was monitored by PCR and active infection defined by more than 1000 UI/ml. CMV-disease was considered when infection and unspecific symptomatology coexisted. Nabs titers were determined by microneutralization assays using the ARPE-19 epithelial cell line. We defined the Nabs titer as the one that reduced virus infectivity by 50% or more compared with the infected control.
Results: Among the 74 analyzed patients, 37 showed CMV viremia (from 0 to 3 month post-Tx) while 37 did not. Twelve out of the 37 patients developed CMV disease. KTR with CMV infection during the first 12 months post-Tx showed pre-Tx diminished cTFH frequency compared to those who did not (0,75 vs 1,19 p= 0,03). Amongst infected patients, those who develop CMV disease had lower pre-Tx cTFH (count and frequency) (p= 0,01 and p= 0,009 respectively).  Pre-Tx numbers of CD4+CXCR5+ cells positively correlated with the time until viral replication appeared which means that those patients with superior cTFH pre-Tx counts suffered the CMV infection later. A proportional hazard model points out that higher proportions of cTFH pre-Tx and 14 days after surgery, is a protective factor for CMV infection with a HR of 0,55 (p=0,04) and 0,46 (p=0,01). However, pre-Tx cTFH numbers did not correlate with pre-Tx Nabs titers, nor patients who presented CMV-infection or disease had lower pre-Tx Nabs titers.
Conclusion: These results suggest that higher pre-Tx cTFH decreases the CMV infection risk in KTR, however, this potential protection does not seem to be mediated by Nabs. Whether cTFH fosters T CD8+ cytolytic activity to protect against CMV is under study