Successful engraftment in recipients of haploidentical stem cells with donor-specific antibodies: role of flow cytometric cross-match

The impact of HLA donor-specific antibodies on engraftment and the evolving desensitization strategies

The majority of contemporary allogeneic hematopoietic stem cell transplantation (HCT) procedures utilize partially HLA-mismatched stem cell grafts. Donor-specific anti-HLA antibodies (DSA) are associated with primary graft failure independent of the graft source, conditioning intensity and other patient and donor factors. Here we provide an update on testing and monitoring of DSA, review the impact of DSA on stem cell engraftment, and present promising desensitization modalities. Ultimately, we attempt to provide practical recommendations for DSA screening and mitigation strategies.

[Definition and standardization of histocompatibility requests depending on patient course and donor type: Guidelines from the Francophone Society of Bone Marrow Transplantation and Cellular Therapy (SFGM-TC) and the Francophone Society of Histocompatibility and Immunogenetics (SFHI)]

Standardization of histocompatibility tests for allogeneic hematopoietic cell transplants, harmonization of information transmitted to clinicians are part of quality improvement and optimization of human and economic resources. New HLA typing technologies provide high-resolution information within a reasonable time frame. Knowledge of high-resolution HLA typing for the patient and their relatives is essential for a better interpretation of compatibilities. HLA-DPB1 typing must be considered in transplant field regardless of the donor type. The benefits of using search and match programs are considerable. It saves time and reduces additional typing costs by providing rapid information about the likelihood to identify a matched unrelated donor. A backup therapy considering alternative cell sources or treatment can therefore be quickly implemented. The importance of knowledge and consideration of patient immunization for donor choice was explored in previous workshops of the SFGM-TC (2018 and 2019). The published recommendations remain applicable. The routine follow-up protocol and in case of desensitization will be detailed here. This harmonization must be accompanied by the standardization of information to be returned to the clinician regarding the donor finding possibilities for the patient. This will guarantee a similar quality level in every center.

Correlation analysis between virtual and Complement-Dependent-Cytotoxicity crossmatch in a monocenter retrospective series of 118 allografted patients

PURPOSE OF THE STUDY

The detection of patients' anti-HLA antibodies before allogeneic hematopoietic stem cell transplantation (HSCT) may affect post-transplant outcome, due to a potential detrimental impact on engraftment or toxicity-related issues. Crossmatch (XM) techniques provide support to physicians during the pre-transplant phase but the role of Complement-Dependent Cytotoxicity XM (CDC-XM) is not well-defined when performed routinely and in parallel with the virtual XM.

PATIENTS AND METHODS

We report here our experience with both virtual and CDC-XM tests on n = 118 patients undergoing search for a donor other than HLA-identical sibling from July 2013 to June 2018 at our Institution. When anti-HLA antibodies (Abs) were present, they were classified as donor-specific Abs (DSA) or non-DSA.

RESULTS

On the n = 118 patients, n = 35 (29.7 %) had a positive virtual XM test (of which one of more DSA were found in n = 8; 6.8 %) and n = 5 had a positive CDC-XM test. These latter, positive for HLA class II only, were interpreted as false-positive results due to prior administration of anti-CD20 to the patients, all affected by lymphoma; none of them had a positive virtual XM for anti-HLA Abs of class II. Importantly, all these patients successfully engrafted, further supporting the lack of significant impact of CDC-XM positive results in this series.

CONCLUSIONS

According to our data on more than a hundred patients, routinely performed CDC-XM does not seem to add significant information with respect to virtual XM. We cannot exclude the usefulness of CDC-XM in specific situations, although a positive CDC-XM result was an unfrequent event.