37 CFR §3.16

Before an allegation of use under either 15 U.S.C. 1051(c) or 15 U.S.C. 1051(d) is filed, an applicant may only assign an application to register a mark under 15 U.S.C. 1051(b) to a successor to the applicant's business, or portion of the business to which the mark pertains, if that business is ongoing and existing.