T cell repertoire development in XSCID dogs following nonconditioned allogeneic bone marrow transplantation

Abstract

Dogs with X-linked severe combined immunodeficiency (XSCID) can be successfully treated by bone marrow transplants (BMT) resulting in full immunologic reconstitution and engraftment of both donor B and T cells without the need for pretransplant conditioning. In this study, we evaluated the T cell diversity in XSCID dogs 4 months to 10.5 years following BMT. At 4 months posttransplantation, when the number of CD45RA+ (naïve) T cells had peaked and plateaued, the T cells in the transplanted dogs showed the same complex, diverse repertoire as those of normal young adult dogs. A decline in T cell diversity became evident approximately 3.5 years posttransplant, but the proportion of Vbeta families showing a polyclonal Gaussian spectratype still predominated up to 7.5 years posttransplant. In 2 dogs evaluated at 7.5 and 10.5 years posttransplant, >75% of the Vbeta families consisted of a skewed or oligoclonal spectratype that was associated with a CD4/CD8 ratio of <0.5. The decline in the complexity of T cell diversity in the transplanted XSCID dogs is similar to that reported for XSCID patients following BMT. However, in contrast to transplanted XSCID boys who show a significant decline in their T cell diversity by 10 to 12 years following BMT, transplanted XSCID dogs maintain a polyclonal, diverse T cell repertoire through midlife.

Figure 1. Classification of TCR Vβ spectratypes

Polyclonal Gaussian distribution (A), polyclonal skewed distribution (B), and oligoclonal distribution (C).

Figure 2. Immunologic reconstitution in XSCID dogs following transplantation with whole bone marrow or CD34⁺ bone marrow cells

Absolute lymphocyte counts (A), proportion of peripheral T cells (B), proportion of peripheral CD45RA⁺ (naïve) T cells (C), CD4/CD8 ratio (D), proliferative response following stimulation with PHA (E), and IgG speficic antibody response following immunization with tetanus toxoid (F).

Figure 3. TCR Vβ spectratypes of normal dogs and XSCID dogs following bone marrow transplantation

The normal dogs are designated with an N and the bone marrow transplanted dogs designated with B. The numbers following the N represent age of the dog in years and the numbers following the B represent the age in years following transplant.

Figure 4. TCR Vβ spectratyping in normal dogs and transplanted XSCID dogs

Each time point represents the summary results from an individual dog. Results are expressed as percentage of total Vβ families representing a polyclonal Gaussian (PG), polyclonal skewed (PS), or oligoclonal (O) phenotype. N-2, N-4, N-7 = normal dogs at 2, 4 and 7 years of age.

Figure 5. TCR Vβ spectratypes of three XSCID dogs three years following initial evaluation

Dog R743 was evaluated at 4.5 years and 7.5 years post transplant. Dog X58 was evaluated at 5.5 years and 8.5 years post transplant. Dog R468 was evaluated at 7.5 years and 10.5 years post transplant.

Figure 6. TCR Vβ spectratyping in three transplanted XSCID dogs at initial testing and three years later

Results are expressed as percentage of total Vβ families representing a polyclonal Gaussian (PG), polyclonal skewed (PS), or oligoclonal (O) phenotype.