Impact of HIV-1 Infection and Antigen Class on T Follicular Helper Cell Responses to Pneumococcal Polysaccharide-Protein Conjugate Vaccine-13

Pneumococcal infections are common and serious complications of HIV-1 disease. Prevention has been compromised by the limited magnitude and quality of Ab responses to T cell-independent type 2 pneumococcal capsular polysaccharides (PPS). The pneumococcal polysaccharide-protein conjugate vaccine-13 (PCV-13) contains PPS conjugated to the T cell-dependent protein (diphtheria toxoid [DT] [CRM197]). We investigated the differential response to PPS and DT by human Ab-secreting B cells (ASC) after immunization with PCV-13 in newly diagnosed healthy HIV⁺ and control adults. The numbers of PPS-specific IgG ASC increased significantly and similarly in HIV⁺ and controls. However, DT-specific IgG ASC increased in controls but not HIV⁺ subjects. To determine the cellular basis of these disparate responses to DT and PPS, we characterized the frequency and activation of T follicular helper (Tfh) cells, the predominant T cell subset providing B cell help. Expression of inducible T cell costimulator (ICOS), which sustains Tfh function and phenotype, increased significantly among controls, when compared with the HIV⁺ group. Increases in ICOS⁺ Tfh correlated with changes in T-dependent, DT-specific IgG ASC in controls but not in HIV⁺ In contrast, ICOS expression did not correlate with T cell-independent type 2 PPS-specific ASC in either group. Of note, upon optimized ex vivo stimulation, CD4 T cells from HIV⁺ subjects differentiated into Tfh cells and formed synapses with Raji B cells at frequencies similar to that of controls. In summary, PCV-13-induced increase in ICOS expression on Tfh was associated with responses to DT, which was compromised in recently diagnosed healthy HIV⁺ adults and can be restored ex vivo by providing effective Tfh-differentiating signals.

Pseudointimal thrombogenicity changes in small arterial grafts

Prosthetic grafts are rapidly covered by blood proteins after implantation. Cellular ingrowth and accumulation of interstitial proteins such as collagen complete the development of graft pseudointima. To investigate the effect of these changes on graft platelet reactivity, indium 111-labeled platelet accumulation on two grafts of differing porosity and thrombogenicity (polytetrafluoroethylene [PTFE] and Dacron) was measured 1, 7, and 21 days after graft implantation in canine carotid arteries. Pseudointima structure, weight, and collagen content were also determined at each measurement interval. In addition, platelet accumulation on carotid autografts and dissected carotid arteries was determined for comparison. Platelet accumulation on all grafts and arteries diminished significantly (p less than 0.05) between 1 and 7 days. Platelet accumulation on autografts and dissected arteries decreased further between 7 and 21 days and approached baseline. In contrast, platelet accumulation on Dacron grafts increased significantly (p less than 0.05) between 7 and 21 days to levels above those measured at 1 day, whereas platelet accumulation in PTFE grafts increased minimally and remained significantly below 1-day levels. A thick pseudointima that contained significant amounts of collagen developed in Dacron grafts during this time period, and a thin, incomplete pseudointima containing minimal collagen covered PTFE grafts. These differences in pseudointimal platelet reactivity and composition were associated with decreased patency of Dacron grafts (78%) compared to PTFE grafts (89%).