CTLA4Ig-mediated blockade of T-cell costimulation in patients with psoriasis vulgaris

Abstract

Engagement of the B7 family of molecules on antigen-presenting cells with their T cell-associated ligands, CD28 and CD152 (cytotoxic T lymphocyte-associated antigen-4 [CTLA-4]), provides a pivotal costimulatory signal in T-cell activation. We investigated the role of the CD28/CD152 pathway in psoriasis in a 26-week, phase I, open-label dose-escalation study. The importance of this pathway in the generation of humoral immune responses to T cell-dependent neoantigens, bacteriophage phiX174 and keyhole limpet hemocyanin, was also evaluated. Forty-three patients with stable psoriasis vulgaris received 4 infusions of the soluble chimeric protein CTLA4Ig (BMS-188667). Forty-six percent of all study patients achieved a 50% or greater sustained improvement in clinical disease activity, with progressively greater effects observed in the highest-dosing cohorts. Improvement in these patients was associated with quantitative reduction in epidermal hyperplasia, which correlated with quantitative reduction in skin-infiltrating T cells. No markedly increased rate of intralesional T-cell apoptosis was identified, suggesting that the decreased number of lesional T cells was probably likely attributable to an inhibition of T-cell proliferation, T-cell recruitment, and/or apoptosis of antigen-specific T cells at extralesional sites. Altered antibody responses to T cell-dependent neoantigens were observed, but immunologic tolerance to these antigens was not demonstrated. This study illustrates the importance of the CD28/CD152 pathway in the pathogenesis of psoriasis and suggests a potential therapeutic use for this novel immunomodulatory approach in an array of T cell-mediated diseases.

Figure 1

Clinical findings representative of a 50% or greater improvement from baseline Physician’s Global Assessment observed in 19 of 41 study patients. Serial photographs are obtained at baseline (left panels), day 36 (middle panels), and day 71 (right panels) in a patient accrued to the CTLA4Ig 50 mg/kg dose level. A maximal improvement of 90%, compared with baseline, was reported for this patient.

Figure 2

Median Physician’s Global Assessment of disease activity in the CTLA4Ig 0.5 mg/kg, 4 mg/kg, and 50 mg/kg dose groups during the study. A significant dose response across the 8 CTLA4Ig treatment groups (P < 0.05) was detected at study weeks 3, 4, 10, 12, and 15; patient numbers were too limited in some dose groups at study weeks 18–26 to allow statistical comparison.

Figure 3

Reversal of molecular markers of epidermal and vascular pathology following administration of CTLA4Ig. Representative immunohistologic findings in the 19 patients demonstrating a 50% or greater improvement in global clinical parameters following administration of CTLA4Ig. Serial biopsies at day 1 (upper row), day 36 (middle row), and day 78 (lower row) obtained from the perimeter of a single representative lesion in a patient accrued to the CTLA4Ig 25 mg/kg dose level. Hematoxylin and eosin–stained sections (labeled H & E in a–c) demonstrate progressive epidermal thinning, diminution in the inflammatory cellular infiltrate, and normalization of keratinocyte maturation on or prior to day 36. Scale bar in a: 100 μm. T cells and proliferating cells present in the psoriatic lesions were detected by immunostaining with mAb’s to CD3 (d–f) and Ki67 nuclear protein (g–i), respectively. A progressive decrease in the number of positively staining cells was evident in the serial biopsies. Expression of keratin 16 (j–l) and α-3 integrin (m–o) in lesional biopsies was reduced following administration of CTLA4Ig. Immunostaining with mAb’s to laminin (p–r), present in the basement membrane of blood vessels, illustrates the serial decrease in the ectasia of the lesional vessels.

Figure 4

Quantitative histologic parameters measured in the 6 patients accrued to the CTLA4Ig 25 mg/kg dose group. In a and b, the number of epidermal CD3⁺ (T) cells and the number of Ki67⁺ (proliferating) keratinocytes per linear millimeter of surface are depicted over the period of observation. In c, the change in epidermal thickness over the first 78 days of the study period is shown. Epidermal thickness was calculated by quantitating the cross-sectional epidermal surface area beneath a 1-mm linear region of a representative histologic section using computer-assisted image analysis. Individual data points are an average derived from triplicate analyses. The mean percent changes at day 78 compared with day 1 in a–c were 82% (P < 0.001), 82% (P = 0.004), and 51% (P = 0.01), respectively. P values were based on a two-sided t test for no change at day 78 compared with day 1.

Figure 5

Absence of increased intralesional apoptosis following administration of CTLA4Ig. Illustrated in a and b are representative negative TUNEL reactions obtained following histochemical examination across all sampling time points and all dose levels of the study. In representative sections from a patient accrued to the 50 mg/kg dose level, no increased rate of in situ cell death was evident when comparisons were made between pretreatment (a) and day 36 (b) lesional biopsies. Scale bar in a: 100 μm. Positive controls included in these experiments are illustrated in c and d, which are paired biopsy specimens from patients receiving ultraviolet B light (UVB) therapy. An increased rate of in situ apoptosis at day 15 (d) compared with baseline examination (c) was seen following daily administration of UVB treatment. Double staining of these sections with mAb’s reactive with CD3 identified the apoptotic cells as T cells.

Figure 6

Reconstitution of the humoral immune response to bacteriophage φX174 in the 1 mg/kg, 4 mg/kg, 16 mg/kg, and 50 mg/kg dosing cohorts following tertiary and quaternary immunization. Bacteriophage φX174 was administered at week 1 (1°), week 5 (2°), week 11 (3°), and week 22 (4°). Patient sera were collected before and 1, 2, and 4 weeks after each administration of bacteriophage. Anti-bacteriophage antibody titers were determined by a neutralizing assay and expressed as a rate of phage inactivation, or K value (Kv). Antibody titers for patients accrued to the 1 mg/kg (a), 4 mg/kg (b), 16 mg/kg (c), and 50 mg/kg (d) dose groups are depicted. The geometric mean Kv’s of the 23 psoriatic control patients are illustrated by the dark black line in each part. Vertical bars indicate ±2 SD of the control group mean Kv. Following tertiary and/or quaternary immunization, all patients’ titers were within 2 SD of the control group primary and secondary responses, respectively, with the exception of 1 patient enrolled in the 50 mg/kg dose group (diamonds in d). Despite progressive titer amplification and a immunoglobulin class switch following the 4° immunization, this patient did not achieve the study definition of full reconstitution of the humoral immune response to bacteriophage φX174.