Which of the following is more likely a cause of secondary immunodeficiency?Immunosuppressive drug taken by organ transplant recipientsWiskott-Aldrich SyndromeMHC class II deficiencySevere combined immunodeficiency

The most likely cause of secondary immunodeficiency from the options provided is the use of immunosuppressive drugs by organ transplant recipients.

Here's why:

1. Secondary immunodeficiency is caused by external factors such as drugs, malnutrition, aging, or diseases like diabetes, HIV, etc. In this case, immunosuppressive drugs taken by organ transplant recipients are used to prevent the body from rejecting the new organ. However, these drugs also suppress the immune system, making the individual more susceptible to infections and diseases, hence causing secondary immunodeficiency.

2. The other options listed - Wiskott-Aldrich Syndrome, MHC class II deficiency, and Severe combined immunodeficiency - are all examples of primary immunodeficiencies. These are caused by genetic defects that disrupt the normal functioning of the immune system, and are present from birth. They are not caused by external factors, and therefore do not fall under the category of secondary immunodeficiency.