Altered thymic CD4(+) T-cell recovery after allogeneic hematopoietic stem cell transplantation is critical for nocardiosis

Purpose of the study: Nocardia affects immunocompromised human host exhibiting an altered cell-mediated immunity. Infectious risk after allogeneic hematopoietic cell transplantation (AHCT) is significantly correlated to the recovery status of donor-derived immune system, especially CD4(+) T-cells reconstitution and thymopoiesis. The purpose of this paper is to highlight a lack of cell-mediated immunity recovery for patients presenting a nocardiosis compared to a control cohort. Patients and methods: This is a case control retrospective monocentric study. We retrospectively analyzed a monocentric cohort of 15 cases of nocardiosis after AHCT and we explored the degree of patients' immunosuppression by phenotyping circulating lymphoid subpopulations, including NK cells, CD8(+) T-cells, CD4(+) T-cells and CD19(+) B-cells. We focused on CD4(+) T-cell subsets to appreciate thymic output, especially on naive CD4(+) T-cells (NTE, CD45RA(+)/RO CD4(+) T-cells) and recent thymic emigrants (RTE, CD4(+)CD45RA(+)/RO/CD31(+). Infected patients were paired with a control cohort of patients with identical transplantation characteristics screened on hematological disease, AHCT conditioning, primary graftversus-host disease (GHVD) prophylaxis, graft type, sex, age, and season at the AHCT and data concerning immunological reconstitution were compared. Results: At onset of nocardiosis, circulating lymphocytes and CD4(+) T-cells means count were respectively 730/mu L and 162/mu L. CD8(+) T-cells, CD56(+) NK cells and CD19(+) B-cells means count were respectively 362/ mu L,160/mu L,112/mu L. CD4(+) T-cells subpopulations, naIve CD4(+) T-cells production was impaired with NTE and RTE means count at 26/syndrome and 11/mu L respectively. Comparison between nocardiosis cohort and control cohort over time highlight significant lower cellular count for lymphocytes, CD4(+) T-cells, NTE and RTE with p = 0.001, p < 0.001, p < 0.001, p < 0.001 respectively. Conclusion: Immune recovery monitoring follow-up after AHCT is of particular importance to identify patients susceptible to develop Nocardiosis. Efficient microbiological investigations toward Nocardia such PCR should be used in case of compatible clinical presentation. (C) 2019 Elsevier Masson SAS. All rights reserved.