Dermatologic and Ophthalmic Drugs Advisory Committee
Questions to the Committee
May 23, 2002
License # STN BL 125036/0 Alefacept
Indication: for the treatment of patients with chronic plaque psoriasis who are candidates for phototherapy or systemic therapy
I. Safety of Alefacept
A. Lymphocyte reduction and risk of infection
Alefacept treatment causes reductions in total lymphocyte counts and T cell subsets. In study 711 (IV study), approximately half of the participants experienced at least a single occurrence of a CD4 cell count below the lower limit of normal at any time during a treatment course (12-week dosing and 12 week follow-up). In study 712 (IM study), this figure was approximately 30%. In some patients, lymphocyte reductions are long lasting. Twelve weeks following the last dose, approximately 20% of study 711 participants had CD4 counts below normal.
The total experience of patients receiving more than 2 cycles is limited. Approximately 50% (N=756) of total alefacept treated patients received 2 courses of treatment, 15% (N=199) received 3 courses, and 10% (N=140) received 4 or more courses. Available data (based on two cycle of treatment) suggest that lymphocyte reductions may be cumulative in some people.
A central issue is whether lymphocyte reductions result in clinical sequelae. In the phase 3 trials, serious infections were reported in 1/413 (0.2%) of placebo and 8/876 (0.9%) of alefacept treated patients. There was no apparent relationship between lymphopenia and infections, and no opportunistic infections were observed. However, some of the infections among patients on alefacept were associated with a protracted course (e.g. cellulitis® septic shock and multi-organ failure, external otitis® facial cellulitis)
The maximum duration of alefacept treatment was 3 months, with a minimum interval of 3 months prior to subsequent dosing. Normal lymphocyte and CD4+ cell counts were required before the first treatment cycle and normal CD4+ cell counts required for subsequent cycles. If licensed, lymphocyte monitoring and dose adjustments may not be as frequent as was performed in the clinical trials. This raises concerns that depth and duration of lymphopenia may be more pronounced, with unknown clinical consequences.
The effects of alefacept on delayed-type hypersensitivity (DTH) were evaluated in two trials, Study 703 (an uncontrolled dose-escalation study) and 708 (a controlled dose-ranging study). Responses to seven microbial antigens applied to non-lesional skin were evaluated. DTH shifts from + to – were observed for isolated antigens (range 0-3 per patient) in study 703 without relationship to dose. In study 708 the number of DTH shifts from + to – was higher in the alefacept groups compared to placebo. There are no reports of patients treated with alefacept who developed tuberculosis. No studies have been performed to evaluate the ability to mount a response to vaccines.
Individuals with severe psoriasis are at higher risk for developing malignancies, particularly skin malignancies (squamous cell carcinoma) and lymphomas. The pathophysiology of the disease and more importantly some of the treatments (PUVA, etc) may predispose to neoplasia. Alefacept is a new biological with known immunosuppressive effects. In the controlled studies, rates of malignancy were: 2/413 (0.5%) for placebo and 10/876 (1.1%) for alefacept treated patients. Most of the malignancies were squamous cell skin cancers though one alefacept treated patient developed B cell lymphoma during an open label extension, and a single occurrence of B cell lymphoma was seen in a non-human primate study.
It is difficult to detect an increase in the rate of malignancies in the absence of larger numbers of patients exposed and longer periods of follow up and in the absence of a concurrent control group.
In the phase 2 study, dosing was weight based. Weight did not appear to be an important factor in the pharmacokinetic profile of alefacept. Thus, the phase 3 studies were conducted using fixed doses for both the IV and IM routes of administration, with the exception that very low weight subjects (< 50kg) received a 30% reduction in the dose. In study 711, efficacy responses were approximately 4 fold less in people weighing >85 kg vs £ 85 (5% vs 19%, respectively after adjusting for placebo effect). Similar trends in response were seen in study 712 (IM study), where response rates for people >85 kg and £ 85 kg were 12% vs 19%, respectively after adjusting for placebo effect. This suggests that heavier study subjects may have been under-dosed; however, such patients appeared to experience a degree of lymphopenia similar to those who were below the weight median.
III. Efficacy Outcomes
In the phase 3 studies the primary assessment was the proportion of patients with >75% improvement in PASI score from baseline. Patients receiving systemic therapy or phototherapy were considered treatment failures in the primary efficacy analysis. Physician’s Global Assessment (PGA) of "clear" or "almost clear" was an important secondary outcome. By PASI assessment, 10-16% (absolute) more alefacept-treated patients responded compared to placebo, and 7-9% (absolute) more alefacept-treated patients responded by PGA assessment.
Of three different instruments used to assess patient reported outcomes, the overall Dermatology Life Quality Index (DLQI) score was considered to be the primary score. The DLQI score ranges from 0 (best) to 30 (worst). The DLQI was measured at baseline and after the end of treatment. The between group difference, which favored alefacept, was no more than 3 points after adjusting for baseline DLQI score.
V. Product Label
The sponsor has proposed that the indicated population be "patients with chronic plaque psoriasis who are candidates for phototherapy or systemic therapy." Eligibility criteria permitted enrollment of individuals who had received prior systemic or phototherapy as well as those who were naïve to such prior therapies.
VI. Studies in Other Populations
A. Adults with other forms of psoriasis
Individuals with erythrodermic, guttate, palmar, plantar pustular, or generalized pustular psoriasis were excluded from the clinical studies.
Pediatric patients have not been evaluated in the clinical development program thus far. Federal regulations require sponsors to conduct trials in pediatric populations for a use approved in adults if the product is to be used in large numbers of affected children or it represents a meaningful therapeutic benefit. Trials in children may be deferred to after market approval for adults, particularly if concerns about toxicity warrant the collection of more safety data in adults before children are exposed. Biogen has requested and received a deferral for the conduct of pediatric studies.
HIV infection was an exclusion criterion. HIV is a precipitating factor in psoriasis.