S.C. Code Ann. § 19-9-120: Witnesses passing through State shall not be subject to arrest or service of process.

If a person passes through this State while going to another state in obedience to a summons to attend and testify in that state or while returning therefrom, he shall not while so passing through this State be subject to arrest or the service of process, civil or criminal, in connection with matters which arose before his entrance into this State under the summons.