TABLE 1.

Monoclonal versus polyclonal preparations

Variable	Antibody prepn
	Monoclonal	Polyclonal
		Immune globulin	Plasma
Specificitya	Single epitope	Multiple epitopes	Multiple epitopes
Isotypeb	Single isotype	Multiple IgG subclasses	Multiple isotypes
Affinityc	Defined	Variable	Variable
Escape variant susceptibilityd	High	Low	Low
Sourcee	Cells	Immune host	Immune host
Serum half-lifef	Defined	Variable	Variable
Costg	High	High	Low
Technical requirementh	High	High	Low
Time to deploymenti	Months to years	Months	Days

^aSpecificity reflects the capacity of an antibody to bind a unique determinant of the antigen. mAbs bind in a single region known as an epitope. Polyclonal preparations include antibodies to many epitopes and thus have multiple specificities.

^bIsotype is conferred by the chemical structure of the constant region of an antibody. IgM, IgG, and IgA are examples of different isotypes; IgG can include more than one subclass (e.g., IgG1, IgG2, etc.). Monoclonal preparations are composed of a single immunoglobulin type and thus have a single isotype and specificity. Polyclonal preparations include multiple types of antibodies. Immune globulin preparations are composed of IgG, which includes several subclasses. Plasma includes all the isotypes generated in the immune response, which can include IgM and IgA in addition to IgG.

^cAffinity refers to the binding strength of the antibody for its respective antigen. For mAb preparations, the affinity is defined by a single immunoglobulin molecule. For polyclonal preparations, the affinity is the average of all the immunoglobulins in solution, and for immune globulin and plasma, the affinity exhibits variability from lot to lot and depending on the donor, respectively.

^dEscape variant susceptibility refers to the ability of a microbe to escape from the host immunity conferred by the antibody preparation. Since mAbs bind to a single epitope, they are susceptible to losing efficacy if a mutation emerges in the epitope that abolishes binding. In contrast, polyclonal preparations are much less susceptible to losing efficacy by selecting for escape variants because they include antibodies recognizing multiple epitopes.

^emAbs are produced by cells in vitro, while polyclonal preparations are generally derived from immune hosts.

^fSerum half-life is the amount of time an antibody is present in the circulation. It is determined by the constant region. Typically, IgG preparations have a half-life of around 3 weeks, although this is a function of the isotype and some patient factors. Since mAb preparations are composed of a single immunoglobulin, the half-life of the antibody is defined by its constant region. For polyclonal preparations, the half-life would represent the average of all immunoglobulins present in the formulation, which in turn would depend on their isotype that is defined by their constant region.

^gmAbs are costly since they are produced by cell culture techniques that require expensive reagents for cell growth and purification. Immune globulin preparations are prepared by fractionating the IgG from immune plasma in industrial facilities. Plasma is the cheapest preparation because it is used directly after it is obtained from a donor with a minimum of processing.

^hmAb and immune globulin preparations require advanced pharmaceutical facilities, while plasma can generated in underresourced regions as evident by the rapid deployment of convalescent plasma against Ebola virus disease.

ⁱmAbs require generation, characterization, and scaling up of production. Thus, using them requires months to years of development prior to clinical deployment. Immune globulin preparations are made from convalescent plasma, which must be available and lot preparation requires months. In contrast, convalescent plasma can be deployed in days, as soon as there are sufficient individuals who have recovered and have adequate antibody responses.