Successful Stem Cell Tranplant Following HLA Identical Sibling Selection Using PGD Combined With HLA Typing In a Case Of CD40 Ligand Deficiency

Pre-Implantation genetic diagnosis and pre implantation Human Leukocyte Antigen (HLA) typing has been successfully used to conceive unaffected HLA identical siblings to provide stem cells for Hematopoietic Stem Cell Transplant (HSCT) (Goussetis, Evgenios, et al. Biology of Blood and Marrow Transplantation 16.3 (2010): 344-349). This technique has been effective in treatment of disease such as Leukemia, Diamond-Blackfan anemia, Thallasemia etc. With improvement of molecular techniques it has been possible to do gene testing from a single cell. We report first case of X-linked Hyper CD40 ligand deficiency where preimplantation genetic diagnosis (PGD) and pre implantation HLA typing were used to achieve successful HSCT from the resulting HLA identical sibling donor. We used dual hematopoietic stem cell sources from cord blood and bone from the nine month old sibling. Currently, patient is 34 months post transplantation doing well with full immunologic reconstitution.

Patient was a 14 month old male who presented with a 2 month history of intermittent fever & poor oral intake. He was drooling excessively and tired on appearance. He had also developed mouth sores and later worsening stridor. Chest x-ray revealed right-sided patchy infiltrates. A laryngoscopy was performed that showed supraglottic stenosis. He was transferred to the PICU where he was intubated, ventilated and treated with 10 days of Meropenem. He was later extubated when it was confirmed that there was healing of the supraglottic area. Patient had Leukopenia and received GCSF. Labs also showed decreased level of IgG, IgA and elevated IgM with low titers to tetanus, H flu and diphtheria vaccines. HIV test was negative. His CD40 ligand test revealed deletion of Exon 2 (Figure 1) confirming the diagnosis. Patient's mother was also confirmed to be a carrier for the mutation. He was started on IVIG supplementation and later subcutaneous Ig.

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When the patient was diagnosed, he had no siblings but his mother was in the first trimester of a pregnancy. HLA typing was done utilizing chorionic villus sampling. Unfortunately, the fetus was found not to be a match and efforts were directed at finding an unrelated donor through multiple donor drives. A well matched unrelated donor was not available after multiple attempts and donor drives for two years. Cord blood transplant and mismatched unrelated donor transplant were considered. Transplants utilizing mismatched unrelated donors for CD40 ligand deficiency are rare and are associated with an increased risk of complications as well as lower overall survival rate. Due to these factors, the parents declined these options for transplant. Parents then decided to pursue PGD with Preimplantation HLA Testing. After PGD and combined HLA testing an unaffected embryo that was a HLA match to the patient was selected after multiple attempts (Figure 2). The mother underwent IVF with the selected embryo and delivered a male sibling. The genetic testing for CD40 ligand deficiency and HLA typing was repeated on the proposed donor baby after birth.

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The repeat tests confirmed that the proposed donor baby was unaffected and a 10 of 10 HLA match for the patient. The patient was subjected to a conditioning regimen consisting of Busulfan, Cytoxan and GVH prophylaxis with Methotrexate and Tacrolimus. Following the regimen, the patient was infused with stem cell dose consisting of fresh bone marrow (1.86x10⁸ TNC/Kg) harvested from the matched sibling donor and cryopreserved cord blood (0.29x10⁸ TNC/Kg) obtained during the sibling donor's birth. The patient was found to be well engrafted (98% on day 18, 100% at 9 months) post transplant. The CD40L test showed 60% CD40L on T cells after stimulation with ICOS (inducible co-stimulator) increased from 0% pre-transplant.

Most patients with hyper CD40 ligand deficiency inherit the causative gene mutation from one of their parents. The average family size in the US is 3.14 (Daphne Lofquist, et al. Households and Families: 2010 Census Briefs).This results in a low probability of finding a sibling donor that is both unaffected and a HLA match. Undergoing multiple pregnancies with low probabilities of conceiving an unaffected HLA matched sibling is stressful, time consuming and ineffective. PGD combined with HLA typing provides an effective way of choosing an embryo that result in a matched HLA donor sibling and subsequent successful stem cell transplant.