Summary of recommendations for monitoring of post-HCT IR. (A) Recommended monitoring for clinical purposes: we recommend monitoring of CD4⁺ T cells, CD8⁺ T cells, NK cells, and B cells, with corresponding time points. Recommended periodic assessment of IgG production until IVIG independence is reached. (B) Additional monitoring for research purposes: several additional T-cell subsets can be monitored in the context of research studies. It is generally advisable to monitor CD4⁺ T-cell subsets when the total number of CD4⁺ T cells exceeds 200/μL. It is also possible to monitor TCR diversity by next-generation sequencing. Finally, it is possible to perform functional assays to evaluate NK cell cytolytic function and cytokine production or to evaluate T-cell proliferative capacity and cytokine response. (C) Additional tests can be performed in clinical setting but are not routinely recommended due to lack of evidence and/or standardized methods. See Table 5 for further details on our recommendations. DTaP, ditpheria tetanus acellular pertussis vaccination; Hib, haemophilus B vaccination; IVIG, IV immunoglobulins; PCV, pneumococcal conjugate vaccine.