Consequences of Antibody and Other Immune Responses

Although rare, immune response to a therapeutic protein may lead to anaphylactic or allergic reactions that require immediate medical attention. Less severe but far more frequent consequences are local injection-site reactions. Neutralizing antibodies in effect reduce the dose of drug available to exert a therapeutic response. Nonneutral-izing antibodies may also reduce biological activity by increasing the size of the resulting protein-antibody complex, which may influence the tissue distribution and clearance of the pharmaceutical protein. Although both mechanisms reduce biological activity, neutralizing antibodies usually result in more severe loss of activity.

An indirect consequence of antibody formation against a therapeutic protein is inhibition of endogenous protein and its functions. For example, if antibody to inter-leukin-2, a T-cell growth factor, is elicited due to administered recombinant IL-2, the neutralizing antibody that blocks the activity of recombinant IL-2 may also neutralize endogenous IL-2 function, which is essential for fighting infections. Another consequence is that patients who have antibodies against a protein drug are not good candidates to receive similar protein products. Immunogenicity data and clinical consequences for some marketed protein products are summarized in Table 5.6.

The FDA advises manufacturers not only to evaluate immunogenicity of new protein products but also to reevaluate immunogenicity on any change in the manufacturing process or target patient population. Understanding of mechanisms leading to induction of immune responses against proteins and other bio-pharmaceuticals will allow the development of strategies appropriate for better control of unintended consequences of immunogenicity [28].

ITABLE 5.6. Immunogenicity of protein pharmaceuticals and clinical consequences

Products"

Frequency (in Humans) Potential or Observed Clinical Effects

Antibodies

Murine (n = 6)b Mouse-human chimeric (n = 3) Humanized Remicade Etanercept

Human urokinase or tissue plasminogen activator

Streptokinase (isolated from bacteria)

Epoetin and G-CSF (human recombinant)

GM-CSF

IL-2

IL-11

15-45% in multiple sclerosis patients 0-25%

None in chronic granulomatous

Less than 1%

Rare

Human against mouse allergic reactions Human against mouse allergic reactions

Human against mouse allergic reactions

Myalgia, rash fever, polyarthralgia

Redness at the sites of previous injections

Neutralizing antibodies (higher incidence with subcutanous route of administration)

Neutralizing antibodies

Rare antibody or allergic reactions

Allergic reaction; increased incidence of binding antibody with recent infection of streptococcus

Binding antibody and allergic reactions

Binding and neutralizing antibodies; allergic reactions

Binding antibodies; but rarely are they neutralizing

Binding antibody; not neutralizing; some local subcutaneous site reactions reported

"Protein products were tested using therapeutic dosing schedules. bNumber of different molecules for the same type of protein surveyed.

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