Unexpected hematologic effects of biotherapeutics in nonclinical species and in humans.

Biotherapeutics are expanding the arsenal of therapeutics available for treating and preventing disease. Although initially thought to have limited side effects due to the specificity of their binding, these drugs have now been shown to have potential for adverse drug reactions including effects on peripheral blood cell counts or function. Hematotoxicity caused by a biotherapeutic can be directly related to the activity of the biotherapeutic or can be indirect and due to autoimmunity, biological cascades, antidrug antibodies, or other immune system responses. Biotherapeutics can cause hematotoxicity primarily as a result of cellular activation, cytotoxicity, drug-dependent and independent immune responses, and sequelae from initiating cytokine and complement cascades.  The underlying pathogenesis of biotherapeutic-induced hematotoxicity often is poorly understood. Nonclinical studies have generally predicted clinical hematotoxicity for recombinant cytokines and growth factors.  However, most hematologic liabilities of biotherapeutics are not based on drug class but are species specific, immune-mediated, and of low incidence. Despite the potential for unexpected hematologic toxicity, the risk-benefit profile of most biotherapeutics is favorable; hematologic effects are readily monitorable and managed by dose modification, drug withdrawal, and/or therapeutic intervention.  This article reviews examples of biotherapeutics that have unexpected hematotoxicity in nonclinical or clinical studies.