This formula will return sum of values in JAN thru the current month. I assumed table is at top of document and to the left.
A values:
=SUM(INDIRECT("B2:"&ADDRESS(2,MONTH(TODAY())+1,4)))
B values:
=SUM(INDIRECT("B3:"&ADDRESS(3,MONTH(TODAY())+1,4)))
C values:
=SUM(INDIRECT("B4:"&ADDRESS(4,MONTH(TODAY())+1,4)))
*EDIT*
To make it more dynamic, say you have in cell "H8" the value 'A' and want to return the A sum up to the current month, you can do it like this:
=SUM(INDIRECT("B"&MATCH(H8,A1:A4,0)&":"&ADDRESS(MATCH(H8,A1:A4,0),MONTH(TODAY())+1,4)))