PURPOSE: GATA2 deficiency, a rare inborn error of immunity, presents with highly variable phenotypes. Bone marrow (BM) changes such as hypocellularity and myelodysplastic syndrome (MDS) are common, with hematopoietic stem cell transplantation being the only curative option due to the risk of progression to acute myeloid leukemia. Although traditional markers like cytogenetic abnormalities and somatic mutations (e.g., ASXL1) identify the risk of leukemic transformation, efforts to identify novel predictors of disease evolution are needed. CD8+ T cells are known to play a key role in MDS immune surveillance, but their specific involvement in GATA2 deficiency remains poorly defined. METHODS: In this case report, we report on a young adult with GATA2 deficiency who underwent longitudinal monitoring of both peripheral and BM lymphocyte subsets, with a focus on CD8+ T-cell evolution in relation to MDS progression. RESULTS: The patient exhibited typical GATA2-deficient immune-hematological findings, including monocytopenia, B- and NK-cell deficiency, but had no history of severe infections and remained transfusion-independent. While peripheral CD8+ T-cell levels remained stable over time, a notable reduction in BM CD8+ T cells was observed in association with MDS progression. CONCLUSION: Providing a long-term follow-up of one GATA2-deficient patient, we suggest that a decrease in BM CD8+ T cells may serve as an early marker of immune surveillance escape and disease progression. These findings underscore the need for further investigation into the role of BM CD8+ T cells in GATA2 deficiency and MDS evolution, potentially offering new insights for follow-up and therapeutic intervention.