Human platelet antigen (HPA)-1a peptides do not reliably suppress anti-HPA-1a responses using a humanized severe combined immunodeficiency (SCID) mouse model

Abstract

SummaryFetal and neonatal alloimmune thrombocytopenia (FNAIT) occurs most frequently when human platelet antigen (HPA)-1a-positive fetal platelets are destroyed by maternal HPA-1a immunoglobulin (Ig)G antibodies. Pregnancies at risk are treated by administration of high-dose intravenous Ig (IVIG) to women, but this is expensive and often not well tolerated. Peptide immunotherapy may be effective for ameliorating some allergic and autoimmune diseases. The HPA-1a/1b polymorphism is Leu/Pro33 on β3 integrin (CD61), and the anti-HPA-1a response is restricted to HPA-1b1b and HLA-DRB3*0101-positive pregnant women with an HPA-1a-positive fetus. We investigated whether or not HPA-1a antigen-specific peptides that formed the T cell epitope could reduce IgG anti-HPA-1a responses, using a mouse model we had developed previously. Peripheral blood mononuclear cells (PBMC) in blood donations from HPA-1a-immunized women were injected intraperitoneally (i.p.) into severe combined immunodeficient (SCID) mice with peptides and HPA-1a-positive platelets. Human anti-HPA-1a in murine plasma was quantitated at intervals up to 15 weeks. HPA-1a-specific T cells in PBMC were identified by proliferation assays. Using PBMC of three donors who had little T cell reactivity to HPA-1a peptides in vitro, stimulation of anti-HPA-1a responses by these peptides occurred in vivo. However, with a second donation from one of these women which, uniquely, had high HPA1a-specific T cell proliferation in vitro, marked suppression of the anti-HPA-1a response by HPA-1a peptides occurred in vivo. HPA-1a peptide immunotherapy in this model depended upon reactivation of HPA-1a T cell responses in the donor. For FNAIT, we suggest that administration of antigen-specific peptides to pregnant women might cause either enhancement or reduction of pathogenic antibodies.

Murine models for studying treatment, prevention and pathogenesis of FNAIT

“…After 2 and 3 weeks, HPA-1a + platelets were injected to boost any present response against the antigen. However, in this system, no consistent effect of this regimen was seen, measured by anti-HPA-1a antibody responses in vivo [47]. This kind of therapeutic strategy still holds potential, but may require additional factors targeting the antigen-presenting cells, other than peptide alone, to induce an effective tolerogenic effect on T cells [48].…”

“…There has also been interest in targeting the T cell response in FNAIT, as the peptide harboring the HPA-1a epitope (the Leu33 residue) is efficiently presented to HPA-1a-specific T cells by antigenpresenting cells expressing the DRA/DRB3*01:01 molecule [40][41][42][43][44][45][46]. Jackson and colleagues made attempts to dampen already established immune responses by tolerization with peptide treatment [47]. In a SCID mice model depleted of NK cells and macrophages, PBMC from HLA-DRB3*01:01-positive HPA-1a alloimmunized women were intraperitoneally injected followed by administration of HPA-1a-derived peptides.…”

Recent progress in understanding the pathogenesis of fetal and neonatal alloimmune thrombocytopenia

“…Jackson et al () examined the ability of HPA‐1a antigen‐specific peptides to reduce IgG anti‐HPA‐1a responses in SCID mice. There is evidence that peptide immunotherapy can be effective in alleviating autoimmune disease and allergies (Larche & Wraith, ; Moldaver & Larche, ).…”

“…Mice were given intraperitoneal injections of peripheral blood mononuclear cells (PBMC) from HPA‐1a‐immunized women together with HPA‐1a peptides (12–22 mers) and HPA‐1a‐positive platelets. Instead of inhibiting, the peptides actually augmented the HPA‐1a antibody response in vivo in the mice using PBMC from three of four women (Jackson et al , ).…”