That's short for Monastic Theological Studies!
Sr. Anna Marie (Elmira) is at the program this year as tutor and has some photos up of the sisters at class. Sr. Mary Amata is somewhere in the room, just not in this photo!
Seated to the left of Sr. Joseph Maria is her name-double, Sr. Mary Guise which is Vietnamese for "Joseph". And of course, behind Sr. Maria Teresa is Sr. Mary Jeremiah, coordinator of the MTS.
You can see more photos on the Elmira Dominican Nuns Blog!