The invention provides compositions for treating or preventing T1D (T1D), the compositions comprising one or more antigen presenting cells (APC) that have been pulsed with one or more bacteria and/or components of the bacteria, wherein the bacteria or their components confer upon the APCs the ability to inhibit the generation of diabetes-promoting T cells. The subject invention also provides a method of treating or preventing T1D in a subject, the method comprising administering APC that have been pulsed with one or more bacteria and/or components of the bacteria and wherein the bacteria or their components confer upon the APCs the ability to inhibit the generation of diabetes-promoting T cells.