Fig. 1. Challenges associated with passive immunization prophylaxis and the desired attributes for an ideal antibody formulation to enable effective prophylaxis. (a) Passive immunization provides protection against infectious disease through direct administration of broadly neutralizing antibodies (bnAbs). (b) Current bnAbs exhibit poor pharmacokinetics and require multiple doses to maintain a protective titer; in addition, (c) most bnAbs are administered by IV infusion, which limits the feasibility of the treatment. (d) Comparing current formulation limitations with those of an ideal formulation, (e) a subcutaneous depot containing bnAbs emerges as a potential solution to current formulation challenges.