Telomeres protect chromosome ends from end-to-end fusion and degradation. Loss of telomere function causes cell-cycle arrest or cell death. Autosomal dominant dyskeratosis congenita (AD DC), a rare inherited bone marrow failure syndrome, is caused by mutations in TERC, the RNA component of telomerase. Here, we studied the telomere dynamics over three generations in a 32-member extended family with AD DC due to a TERC gene deletion. Our analysis shows that peripheral blood cells from family members haploinsufficient for TERC have very short telomeres. Telomeres are equally short in all individuals carrying the TERC gene deletion irrespective of their age. Chromosome-specific telomere analysis distinguishing the parental origin of telomeres showed that in gene deletion carriers, paternal and maternal telomeres are similarly short and similar in length to those of the affected parent. In children of affected parents who have normal TERC genes, parental telomeres are again similar in length, but two generations appear to be necessary to fully restore normal telomere length. These results are consistent with a model in which telomerase preferentially acts on the shortest telomeres. When TERC is limiting, this preference leads to the accelerated shortening of longer telomeres. The limited amount of active telomerase in TERC RNA haploinsufficiency may not be able to maintain the minimal length of the increasing number of short telomeres. Thus, the number of cells with excessively short telomeres and the degree of residual telomerase activity may determine the onset of disease in patients with AD DC. dyskeratosis congenita ͉ anticipation ͉ quantitative-FISH

B cells appear to play a role in chronic graft-versus-host disease (cGVHD) as shown in murine models and the success of anti-CD20 B cell antibody treatment in humans. Recent studies have shown that immunostimulatory microbial CpG-DNA splenic responses were enhanced in murine GVHD. We hypothesized that CpG-induced B cell responses are increased in human cGVHD. Newly diagnosed cGVHD patients enrolled on the COG protocol ASCT0031 were divided into early (3-8 months postblood and marrow transplant [BMT]) and late (> or =9 months post-BMT) onset groups and compared to time-matched control BMT patients. A significantly greater percentage of phosphorothioate (PS)-modified CpG stimulated B cells from cGVHD patients demonstrated an increased expression of CD86 compared to controls (P = .0004). This response had a significant correlation between B cell TLR9 expression (r(2) = 0.65; P = .002) and CD86 upregulation using the entirely TLR9-dependent native phosphodiester CpG (P = .003). The PS-modified CpG response at 2 months after initiation of cGVHD therapy demonstrated a trend toward predicting therapeutic response at 9 months post-BMT (P = .07). These findings suggest that an increased number of B cells, primed for a TLR9 response, may play a role in the pathophysiology of cGVHD.

We prospectively studied immune reconstitution in 102 children who underwent T-lymphocyte depleted bone marrow transplants using either closely matched unrelated donors or partially matched familial donors by assaying total lymphocyte counts (TLC), T-cell subsets, B cells, and natural killer cells. TLC, CD3+, and CD4+ T-cell counts remained depressed until 2 to 3 years posttransplant, whereas CD8+ T-cell counts normalized by 18 months, resulting in an inverted CD4:CD8 ratio until 12 months posttransplant. Although the percentage of NK cells was elevated early posttransplant, their absolute numbers remained normal. CD20+ B cells were depressed until 12 to 18 months posttransplant. Factors affecting immunophenotypic recovery were analyzed by nonparametric statistics. Younger patients tended to have higher TLC posttransplant. Higher marrow cell doses were not associated with hastened immunophenotypic recovery. Graft-versus-host disease (GVHD) and/or its treatment significantly delayed the immune reconstitution of CD3+, CD4+, and CD20+ cells. The presence of cytomegalovirus was associated with increased CD8+ counts and a decrease in the percentages of CD4+ and CD20+ cells.